fix(util): properly determine viewport top offset

* Properly determines the viewport top offset, without any consistency issues for the `scrollTop`.
* The `scrollTop` method had a wrong name when passing an element, because it resolved the client rects in relative to the viewport.
* Now it determines the viewport top offset from the window (instead of using the body element - this is deprecated)

Fixes angular#9370.

src/components/autocomplete/js/autocompleteController.js

@@ -113,9 +113,11 @@ function MdAutocompleteCtrl ($scope, $element, $mdUtil, $mdConstant, $mdTheming,
       styles.bottom    = bot + 'px';
       styles.maxHeight = Math.min(MAX_HEIGHT, hrect.top - root.top - MENU_PADDING) + 'px';
     } else {
+      var bottomSpace = root.bottom - hrect.bottom - MENU_PADDING + $mdUtil.getViewportTop();
+
       styles.top       = (top - offset) + 'px';
       styles.bottom    = 'auto';
-      styles.maxHeight = Math.min(MAX_HEIGHT, root.bottom + $mdUtil.scrollTop() - hrect.bottom - MENU_PADDING) + 'px';
+      styles.maxHeight = Math.min(MAX_HEIGHT, bottomSpace) + 'px';
     }
 
     elements.$.scrollContainer.css(styles);

src/components/dialog/dialog.js

@@ -1164,8 +1164,11 @@ function MdDialogProvider($$interimElementProvider) {
         height: container.css('height')
       };
 
+      // If the body is fixed, determine the position of the parent in relative to the viewport.
+      var parentTop = $mdUtil.getViewportTop() + options.parent[0].getBoundingClientRect().top;
+
       container.css({
-        top: (isFixed ? $mdUtil.scrollTop(options.parent) : 0) + 'px',
+        top: (isFixed ? parentTop : 0) + 'px',
         height: height ? height + 'px' : '100%'
       });
 

src/components/input/input.js

@@ -569,7 +569,8 @@ function inputTextareaDirective($mdUtil, $window, $mdAria, $timeout, $mdGesture)
 
         function onDrag(ev) {
           if (!isDragging) return;
-          element.css('height', startHeight + (ev.pointer.y - dragStart) - $mdUtil.scrollTop() + 'px');
+
+          element.css('height', (startHeight + ev.pointer.distanceY) + 'px');
         }
 
         function onDragEnd(ev) {

src/core/util/util.js

@@ -133,18 +133,12 @@ function UtilFactory($document, $timeout, $compile, $rootScope, $$mdAnimate, $in
     },
 
     /**
-     * Calculate the positive scroll offset
-     * TODO: Check with pinch-zoom in IE/Chrome;
-     *       https://code.google.com/p/chromium/issues/detail?id=496285
+     * Determines the absolute position of the viewport.
+     * Useful when making client rectangles absolute.
+     * @returns {number}
      */
-    scrollTop: function(element) {
-      element = angular.element(element || $document[0].body);
-
-      var body = (element[0] == $document[0].body) ? $document[0].body : undefined;
-      var scrollTop = body ? body.scrollTop + body.parentElement.scrollTop : 0;
-
-      // Calculate the positive scroll offset
-      return scrollTop || Math.abs(element[0].getBoundingClientRect().top);
+    getViewportTop: function() {
+      return window.scrollY || window.pageYOffset || 0;
     },
 
     /**
@@ -251,37 +245,39 @@ function UtilFactory($document, $timeout, $compile, $rootScope, $$mdAnimate, $in
 
       // Converts the body to a position fixed block and translate it to the proper scroll position
       function disableBodyScroll() {
-        var htmlNode = body.parentNode;
-        var restoreHtmlStyle = htmlNode.style.cssText || '';
-        var restoreBodyStyle = body.style.cssText || '';
-        var scrollOffset = $mdUtil.scrollTop(body);
+        var documentElement = $document[0].documentElement;
+
+        var prevDocumentStyle = documentElement.style.cssText || '';
+        var prevBodyStyle = body.style.cssText || '';
+
+        var viewportTop = $mdUtil.getViewportTop();
         var clientWidth = body.clientWidth;
 
         if (body.scrollHeight > body.clientHeight + 1) {
-          applyStyles(body, {
+
+          angular.element(body).css({
             position: 'fixed',
             width: '100%',
-            top: -scrollOffset + 'px'
+            top: -viewportTop + 'px'
           });
 
-          htmlNode.style.overflowY = 'scroll';
+          documentElement.style.overflowY = 'scroll';
         }
 
-        if (body.clientWidth < clientWidth) applyStyles(body, {overflow: 'hidden'});
+        if (body.clientWidth < clientWidth) {
+          body.style.overflow = 'hidden';
+        }
 
         return function restoreScroll() {
-          body.style.cssText = restoreBodyStyle;
-          htmlNode.style.cssText = restoreHtmlStyle;
-          body.scrollTop = scrollOffset;
-          htmlNode.scrollTop = scrollOffset;
+          // Reset the inline style CSS to the previous.
+          body.style.cssText = prevBodyStyle;
+          documentElement.style.cssText = prevDocumentStyle;
+
+          // The body loses its scroll position while being fixed.
+          body.scrollTop = viewportTop;
         };
       }
 
-      function applyStyles(el, styles) {
-        for (var key in styles) {
-          el.style[key] = styles[key];
-        }
-      }
     },
     enableScrolling: function() {
       var method = this.disableScrollAround._enableScrolling;

src/core/util/util.spec.js

@@ -223,10 +223,33 @@ describe('util', function() {
         // Restore the scrolling.
         enableScrolling();
         window.scrollTo(0, 0);
-        document.body.removeChild(element[0]);
+
+        element.remove();
       }));
     });
 
+    describe('getViewportTop', function() {
+
+      it('should properly determine the top offset', inject(function($mdUtil) {
+        var element = angular.element('<div style="height: 2000px">');
+
+        document.body.appendChild(element[0]);
+
+        // Scroll down to 1000px y-axis.
+        window.scrollTo(0, 1000);
+
+        expect($mdUtil.getViewportTop()).toBe(1000);
+
+        // Restore the scrolling.
+        window.scrollTo(0, 0);
+
+        expect($mdUtil.getViewportTop()).toBe(0);
+
+        element.remove();
+      }));
+
+    });
+
     describe('nextTick', function() {
       it('should combine multiple calls into a single digest', inject(function($mdUtil, $rootScope, $timeout) {
         var digestWatchFn = jasmine.createSpy('watchFn');