feat(autocomplete): allow developers to specify amount of dropdown items

src/components/autocomplete/autocomplete.scss

@@ -1,4 +1,5 @@
-$autocomplete-option-height: 48px !default;
+// The default item height is also specified in the JavaScript.
+$md-autocomplete-item-height: 48px !default;
 
 @keyframes md-autocomplete-list-out {
   0% {
@@ -201,25 +202,24 @@ md-autocomplete {
 .md-virtual-repeat-container.md-autocomplete-suggestions-container {
   position: absolute;
   box-shadow: 0 2px 5px rgba(black, 0.25);
-  height: 41px * 5.5;
-  max-height: 41px * 5.5;
   z-index: $z-index-tooltip;
 }
 
 .md-virtual-repeat-container.md-not-found {
-  height: 48px;
+  height: $md-autocomplete-item-height;
 }
 
 .md-autocomplete-suggestions {
   margin: 0;
   list-style: none;
   padding: 0;
+
   li {
     font-size: 14px;
     overflow: hidden;
     padding: 0 15px;
-    line-height: $autocomplete-option-height;
-    height: $autocomplete-option-height;
+    line-height: $md-autocomplete-item-height;
+    height: $md-autocomplete-item-height;
     transition: background 0.15s linear;
     margin: 0;
     white-space: nowrap;

src/components/autocomplete/autocomplete.spec.js

@@ -1736,6 +1736,26 @@ describe('<md-autocomplete>', function() {
 
   describe('dropdown position', function() {
 
+    var DEFAULT_MAX_ITEMS = 5;
+    var DEFAULT_ITEM_HEIGHT = 48;
+
+    var dropdownItems = DEFAULT_MAX_ITEMS;
+
+    /**
+     * Function to create fake matches with the given dropdown items.
+     * Useful when running tests against the dropdown max items calculations.
+     * @returns {Array} Fake matches.
+     */
+    function fakeItemMatch() {
+       var matches = [];
+
+      for (var i = 0; i < dropdownItems; i++) {
+        matches.push('Item ' + i);
+      }
+
+      return matches;
+    }
+
     it('should adjust the width when the window resizes', inject(function($timeout, $window) {
       var scope = createScope();
 
@@ -1936,6 +1956,104 @@ describe('<md-autocomplete>', function() {
       document.body.removeChild(parent[0]);
     }));
 
+    it('should calculate the height from the default max items', inject(function($timeout) {
+      var scope = createScope();
+
+      scope.match = fakeItemMatch;
+
+      var template =
+        '<div>' +
+          '<md-autocomplete ' +
+              'md-search-text="searchText" ' +
+              'md-items="item in match(searchText)" ' +
+              'md-item-text="item" ' +
+              'md-min-length="0" ' +
+              'placeholder="placeholder">' +
+            '<span md-highlight-text="searchText">{{item}}</span>' +
+          '</md-autocomplete>' +
+        '</div>';
+
+      var parent = compile(template, scope);
+      var element = parent.find('md-autocomplete');
+      var ctrl = element.controller('mdAutocomplete');
+
+      // Add container to the DOM to be able to test the rect calculations.
+      document.body.appendChild(parent[0]);
+
+      $timeout.flush();
+
+      // Focus the autocomplete and trigger a query to be able to open the dropdown.
+      ctrl.focus();
+      scope.$apply('searchText = "Query 1"');
+      waitForVirtualRepeat(element);
+
+      var scrollContainer = document.body.querySelector('.md-virtual-repeat-container');
+
+      expect(scrollContainer).toBeTruthy();
+      expect(scrollContainer.style.maxHeight).toBe(DEFAULT_MAX_ITEMS * DEFAULT_ITEM_HEIGHT + 'px');
+
+      dropdownItems = 6;
+
+      // Trigger a new query to request an update of the items and dropdown.
+      scope.$apply('searchText = "Query 2"');
+
+      // The dropdown should not increase its height because of the new extra item.
+      expect(scrollContainer.style.maxHeight).toBe(DEFAULT_MAX_ITEMS * DEFAULT_ITEM_HEIGHT + 'px');
+
+      document.body.removeChild(parent[0]);
+    }));
+
+    it('should calculate its height from the specified max items', inject(function($timeout) {
+      var scope = createScope();
+      var maxDropdownItems = 2;
+
+      // Set the current dropdown items to the new maximum.
+      dropdownItems = maxDropdownItems;
+      scope.match = fakeItemMatch;
+
+      var template =
+        '<div>' +
+            '<md-autocomplete ' +
+            'md-search-text="searchText" ' +
+            'md-items="item in match(searchText)" ' +
+            'md-item-text="item" ' +
+            'md-min-length="0" ' +
+            'md-dropdown-items="' + maxDropdownItems +'"' +
+            'placeholder="placeholder">' +
+          '<span md-highlight-text="searchText">{{item}}</span>' +
+        '</md-autocomplete>' +
+        '</div>';
+
+      var parent = compile(template, scope);
+      var element = parent.find('md-autocomplete');
+      var ctrl = element.controller('mdAutocomplete');
+
+      // Add container to the DOM to be able to test the rect calculations.
+      document.body.appendChild(parent[0]);
+
+      $timeout.flush();
+
+      // Focus the autocomplete and trigger a query to be able to open the dropdown.
+      ctrl.focus();
+      scope.$apply('searchText = "Query 1"');
+      waitForVirtualRepeat(element);
+
+      var scrollContainer = document.body.querySelector('.md-virtual-repeat-container');
+
+      expect(scrollContainer).toBeTruthy();
+      expect(scrollContainer.style.maxHeight).toBe(maxDropdownItems * DEFAULT_ITEM_HEIGHT + 'px');
+
+      dropdownItems = 6;
+
+      // Trigger a new query to request an update of the items and dropdown.
+      scope.$apply('searchText = "Query 2"');
+
+      // The dropdown should not increase its height because of the new extra item.
+      expect(scrollContainer.style.maxHeight).toBe(maxDropdownItems * DEFAULT_ITEM_HEIGHT + 'px');
+
+      document.body.removeChild(parent[0]);
+    }));
+
   });
 
   describe('md-highlight-text', function() {

src/components/autocomplete/js/autocompleteController.js

@@ -2,8 +2,8 @@ angular
     .module('material.components.autocomplete')
     .controller('MdAutocompleteCtrl', MdAutocompleteCtrl);
 
-var ITEM_HEIGHT   = 41,
-    MAX_HEIGHT    = 5.5 * ITEM_HEIGHT,
+var ITEM_HEIGHT   = 48,
+    MAX_ITEMS     = 5,
     MENU_PADDING  = 8,
     INPUT_PADDING = 2; // Padding provided by `md-input-container`
 
@@ -92,7 +92,12 @@ function MdAutocompleteCtrl ($scope, $element, $mdUtil, $mdConstant, $mdTheming,
    * @returns {*}
    */
   function positionDropdown () {
-    if (!elements) return $mdUtil.nextTick(positionDropdown, false, $scope);
+    if (!elements) {
+      return $mdUtil.nextTick(positionDropdown, false, $scope);
+    }
+
+    var dropdownHeight = ($scope.dropdownItems || MAX_ITEMS) * ITEM_HEIGHT;
+
     var hrect  = elements.wrap.getBoundingClientRect(),
         vrect  = elements.snap.getBoundingClientRect(),
         root   = elements.root.getBoundingClientRect(),
@@ -112,14 +117,14 @@ function MdAutocompleteCtrl ($scope, $element, $mdUtil, $mdConstant, $mdTheming,
       minWidth: width + 'px',
       maxWidth: Math.max(hrect.right - root.left, root.right - hrect.left) - MENU_PADDING + 'px'
     };
-    if (top > bot && root.height - hrect.bottom - MENU_PADDING < MAX_HEIGHT) {
+    if (top > bot && root.height - hrect.bottom - MENU_PADDING < dropdownHeight) {
       styles.top       = 'auto';
       styles.bottom    = bot + 'px';
-      styles.maxHeight = Math.min(MAX_HEIGHT, hrect.top - root.top - MENU_PADDING) + 'px';
+      styles.maxHeight = Math.min(dropdownHeight, hrect.top - root.top - MENU_PADDING) + 'px';
     } else {
       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(dropdownHeight, root.bottom + $mdUtil.scrollTop() - hrect.bottom - MENU_PADDING) + 'px';
     }
 
     elements.$.scrollContainer.css(styles);

src/components/autocomplete/js/autocompleteDirective.js

@@ -82,6 +82,10 @@ angular
  *     will select on case-insensitive match
  * @param {string=} md-escape-options Override escape key logic. Default is `blur clear`.<br/>
  *     Options: `blur | clear`, `none`
+ * @param {string=} md-dropdown-items Specifies the maximum amount of items to be shown in
+ *     the dropdown.<br/><br/>
+ *     When the dropdown doesn't fit into the viewport, the dropdown will shrink
+ *     as less as possible.
  *
  * @usage
  * ### Basic Example
@@ -165,7 +169,8 @@ function MdAutocomplete ($$mdSvgRegistry) {
       autoselect:       '=?mdAutoselect',
       menuClass:        '@?mdMenuClass',
       inputId:          '@?mdInputId',
-      escapeOptions:    '@?mdEscapeOptions'
+      escapeOptions:    '@?mdEscapeOptions',
+      dropdownItems:    '=?mdDropdownItems'
     },
     link: function(scope, element, attrs, controller) {
       // Retrieve the state of using a md-not-found template by using our attribute, which will