[SPARK-2384] Add tooltips to UI.

This patch adds tooltips to clarify some points of confusion in the UI.  When users mouse over some of the table headers (shuffle read, write, and input size) as well as over the "scheduler delay" metric shown for each stage, a black tool tip (see image below) pops up describing the metric in more detail.  After the tooltip mechanism is added by this commit, I imagine others may want to add more tooltips for other things in the UI, but I think this is a good starting point.

![tooltip](https://cloud.githubusercontent.com/assets/1108612/3491905/994e179e-059f-11e4-92f2-c6c12d248d81.jpg)

This looks scary-big but much of it is adding the bootstrap tool tip JavaScript.

Also I have no idea what to put for the license in tooltip (I left it the same -- the Twitter apache header) or for JQuery (left it as nothing) -- @mateiz what's the right thing here?

cc @pwendell @andrewor14 @rxin

Author: Kay Ousterhout <kayousterhout@gmail.com>

Closes apache#1314 from kayousterhout/tooltips and squashes the following commits:

19981b5 [Kay Ousterhout] Exclude non-licensed javascript files from style check
d9ab5a9 [Kay Ousterhout] Response to Andrew's review
7752449 [Kay Ousterhout] [SPARK-2384] Add tooltips to UI.

.rat-excludes

@@ -22,6 +22,8 @@ slaves
 spark-env.sh
 spark-env.sh.template
 log4j-defaults.properties
+bootstrap-tooltip.js
+jquery-1.11.1.min.js
 sorttable.js
 .*txt
 .*json

core/src/main/resources/org/apache/spark/ui/static/bootstrap-tooltip.js

@@ -0,0 +1,288 @@
+/* ===========================================================
+ * bootstrap-tooltip.js v2.2.2
+ * http://twitter.github.com/bootstrap/javascript.html#tooltips
+ * Inspired by the original jQuery.tipsy by Jason Frame
+ * ===========================================================
+ * Copyright 2012 Twitter, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * ========================================================== */
+
+
+!function ($) {
+
+  "use strict"; // jshint ;_;
+
+
+ /* TOOLTIP PUBLIC CLASS DEFINITION
+  * =============================== */
+
+  var Tooltip = function (element, options) {
+    this.init('tooltip', element, options)
+  }
+
+  Tooltip.prototype = {
+
+    constructor: Tooltip
+
+  , init: function (type, element, options) {
+      var eventIn
+        , eventOut
+
+      this.type = type
+      this.$element = $(element)
+      this.options = this.getOptions(options)
+      this.enabled = true
+
+      if (this.options.trigger == 'click') {
+        this.$element.on('click.' + this.type, this.options.selector, $.proxy(this.toggle, this))
+      } else if (this.options.trigger != 'manual') {
+        eventIn = this.options.trigger == 'hover' ? 'mouseenter' : 'focus'
+        eventOut = this.options.trigger == 'hover' ? 'mouseleave' : 'blur'
+        this.$element.on(eventIn + '.' + this.type, this.options.selector, $.proxy(this.enter, this))
+        this.$element.on(eventOut + '.' + this.type, this.options.selector, $.proxy(this.leave, this))
+      }
+
+      this.options.selector ?
+        (this._options = $.extend({}, this.options, { trigger: 'manual', selector: '' })) :
+        this.fixTitle()
+    }
+
+  , getOptions: function (options) {
+      options = $.extend({}, $.fn[this.type].defaults, options, this.$element.data())
+
+      if (options.delay && typeof options.delay == 'number') {
+        options.delay = {
+          show: options.delay
+        , hide: options.delay
+        }
+      }
+
+      return options
+    }
+
+  , enter: function (e) {
+      var self = $(e.currentTarget)[this.type](this._options).data(this.type)
+
+      if (!self.options.delay || !self.options.delay.show) return self.show()
+
+      clearTimeout(this.timeout)
+      self.hoverState = 'in'
+      this.timeout = setTimeout(function() {
+        if (self.hoverState == 'in') self.show()
+      }, self.options.delay.show)
+    }
+
+  , leave: function (e) {
+      var self = $(e.currentTarget)[this.type](this._options).data(this.type)
+
+      if (this.timeout) clearTimeout(this.timeout)
+      if (!self.options.delay || !self.options.delay.hide) return self.hide()
+
+      self.hoverState = 'out'
+      this.timeout = setTimeout(function() {
+        if (self.hoverState == 'out') self.hide()
+      }, self.options.delay.hide)
+    }
+
+  , show: function () {
+      var $tip
+        , inside
+        , pos
+        , actualWidth
+        , actualHeight
+        , placement
+        , tp
+
+      if (this.hasContent() && this.enabled) {
+        $tip = this.tip()
+        this.setContent()
+
+        if (this.options.animation) {
+          $tip.addClass('fade')
+        }
+
+        placement = typeof this.options.placement == 'function' ?
+          this.options.placement.call(this, $tip[0], this.$element[0]) :
+          this.options.placement
+
+        inside = /in/.test(placement)
+
+        $tip
+          .detach()
+          .css({ top: 0, left: 0, display: 'block' })
+          .insertAfter(this.$element)
+
+        pos = this.getPosition(inside)
+
+        actualWidth = $tip[0].offsetWidth
+        actualHeight = $tip[0].offsetHeight
+
+        switch (inside ? placement.split(' ')[1] : placement) {
+          case 'bottom':
+            tp = {top: pos.top + pos.height, left: pos.left + pos.width / 2 - actualWidth / 2}
+            break
+          case 'top':
+            tp = {top: pos.top - actualHeight, left: pos.left + pos.width / 2 - actualWidth / 2}
+            break
+          case 'left':
+            tp = {top: pos.top + pos.height / 2 - actualHeight / 2, left: pos.left - actualWidth}
+            break
+          case 'right':
+            tp = {top: pos.top + pos.height / 2 - actualHeight / 2, left: pos.left + pos.width}
+            break
+        }
+
+        $tip
+          .offset(tp)
+          .addClass(placement)
+          .addClass('in')
+      }
+    }
+
+  , setContent: function () {
+      var $tip = this.tip()
+        , title = this.getTitle()
+
+      $tip.find('.tooltip-inner')[this.options.html ? 'html' : 'text'](title)
+      $tip.removeClass('fade in top bottom left right')
+    }
+
+  , hide: function () {
+      var that = this
+        , $tip = this.tip()
+
+      $tip.removeClass('in')
+
+      function removeWithAnimation() {
+        var timeout = setTimeout(function () {
+          $tip.off($.support.transition.end).detach()
+        }, 500)
+
+        $tip.one($.support.transition.end, function () {
+          clearTimeout(timeout)
+          $tip.detach()
+        })
+      }
+
+      $.support.transition && this.$tip.hasClass('fade') ?
+        removeWithAnimation() :
+        $tip.detach()
+
+      return this
+    }
+
+  , fixTitle: function () {
+      var $e = this.$element
+      if ($e.attr('title') || typeof($e.attr('data-original-title')) != 'string') {
+        $e.attr('data-original-title', $e.attr('title') || '').attr('title', '')
+      }
+    }
+
+  , hasContent: function () {
+      return this.getTitle()
+    }
+
+  , getPosition: function (inside) {
+      return $.extend({}, (inside ? {top: 0, left: 0} : this.$element.offset()), {
+        width: this.$element[0].offsetWidth
+      , height: this.$element[0].offsetHeight
+      })
+    }
+
+  , getTitle: function () {
+      var title
+        , $e = this.$element
+        , o = this.options
+
+      title = $e.attr('data-original-title')
+        || (typeof o.title == 'function' ? o.title.call($e[0]) :  o.title)
+
+      return title
+    }
+
+  , tip: function () {
+      return this.$tip = this.$tip || $(this.options.template)
+    }
+
+  , validate: function () {
+      if (!this.$element[0].parentNode) {
+        this.hide()
+        this.$element = null
+        this.options = null
+      }
+    }
+
+  , enable: function () {
+      this.enabled = true
+    }
+
+  , disable: function () {
+      this.enabled = false
+    }
+
+  , toggleEnabled: function () {
+      this.enabled = !this.enabled
+    }
+
+  , toggle: function (e) {
+      var self = $(e.currentTarget)[this.type](this._options).data(this.type)
+      self[self.tip().hasClass('in') ? 'hide' : 'show']()
+    }
+
+  , destroy: function () {
+      this.hide().$element.off('.' + this.type).removeData(this.type)
+    }
+
+  }
+
+
+ /* TOOLTIP PLUGIN DEFINITION
+  * ========================= */
+
+  var old = $.fn.tooltip
+
+  $.fn.tooltip = function ( option ) {
+    return this.each(function () {
+      var $this = $(this)
+        , data = $this.data('tooltip')
+        , options = typeof option == 'object' && option
+      if (!data) $this.data('tooltip', (data = new Tooltip(this, options)))
+      if (typeof option == 'string') data[option]()
+    })
+  }
+
+  $.fn.tooltip.Constructor = Tooltip
+
+  $.fn.tooltip.defaults = {
+    animation: true
+  , placement: 'top'
+  , selector: false
+  , template: '<div class="tooltip"><div class="tooltip-arrow"></div><div class="tooltip-inner"></div></div>'
+  , trigger: 'hover'
+  , title: ''
+  , delay: 0
+  , html: false
+  }
+
+
+ /* TOOLTIP NO CONFLICT
+  * =================== */
+
+  $.fn.tooltip.noConflict = function () {
+    $.fn.tooltip = old
+    return this
+  }
+
+}(window.jQuery);
+

core/src/main/resources/org/apache/spark/ui/static/initialize-tooltips.js

@@ -0,0 +1,21 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+$(document).ready(function(){
+   $("[data-toggle=tooltip]").tooltip({container: 'body'});
+});
+

core/src/main/resources/org/apache/spark/ui/static/webui.css

@@ -112,3 +112,8 @@ pre {
   padding-bottom: 0;
   border: none;
 }
+
+.tooltip {
+ font-weight: normal;
+}
+

core/src/main/scala/org/apache/spark/ui/ToolTips.scala

@@ -0,0 +1,34 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.ui
+
+private[spark] object ToolTips {
+  val SCHEDULER_DELAY =
+    """Scheduler delay includes time to ship the task from the scheduler to
+       the executor, and time the time to send a message from the executor to the scheduler stating
+       that the task has completed. When the scheduler becomes overloaded, task completion messages
+       become queued up, and scheduler delay increases."""
+
+  val INPUT = "Bytes read from Hadoop or from Spark storage."
+
+  val SHUFFLE_WRITE = "Bytes written to disk in order to be read by a shuffle in a future stage."
+
+  val SHUFFLE_READ =
+    """Bytes read from remote executors. Typically less than shuffle write bytes
+       because this does not include shuffle data read locally."""
+}