fix(tabs): Fix 0-height animation on iOS devices.

On iOS devices, when switching between tabs, the height would jump
to 0, then animate to the proper place causing a bad glitch.

Fixes #4339. Closes #4341.

src/components/tabs/js/tabsController.js

@@ -6,7 +6,7 @@ angular
  * @ngInject
  */
 function MdTabsController ($scope, $element, $window, $mdConstant, $mdTabInkRipple,
-                           $mdUtil, $animate, $attrs, $compile, $mdTheming) {
+                           $mdUtil, $animateCss, $attrs, $compile, $mdTheming) {
   // define private properties
   var ctrl      = this,
       locked    = false,
@@ -635,17 +635,41 @@ function MdTabsController ($scope, $element, $window, $mdConstant, $mdTabInkRipp
         newHeight     = contentHeight + tabsHeight,
         currentHeight = $element.prop('clientHeight');
     if (currentHeight === newHeight) return;
+
+    // Lock during animation so the user can't change tabs
     locked = true;
-    $animate
-        .animate(
-        $element,
-        { height: currentHeight + 'px' },
-        { height: newHeight + 'px' }
-    )
-        .then(function () {
-                $element.css('height', '');
-                locked = false;
-              });
+
+    var fromHeight = { height: currentHeight + 'px'},
+        toHeight = { height: newHeight + 'px' };
+
+    // Set the height to the current, specific pixel height to fix a bug on iOS where the height
+    // first animates to 0, then back to the proper height causing a visual glitch
+    $element.css(fromHeight);
+
+    // Animate the height from the old to the new
+    $animateCss($element, {
+      from: fromHeight,
+      to: toHeight,
+      easing: 'cubic-bezier(0.35, 0, 0.25, 1)',
+      duration: 0.5
+    }).start().done(function () {
+      // Then (to fix the same iOS issue as above), disable transitions and remove the specific
+      // pixel height so the height can size with browser width/content changes, etc.
+      $element.css({
+        transition: 'none',
+        height: ''
+      });
+
+      // In the next tick, re-allow transitions (if we do it all at once, $element.css is "smart"
+      // enough to batch it for us instead of doing it immediately, which undoes the original
+      // transition: none)
+      $mdUtil.nextTick(function() {
+        $element.css('transition', '');
+      });
+
+      // And unlock so tab changes can occur
+      locked = false;
+    });
   }
 
   /**

src/components/tabs/tabs.scss

@@ -31,9 +31,6 @@ md-tabs {
   overflow: hidden;
   position: relative;
   flex-shrink: 0;
-  &.ng-animate {
-    transition: height $swift-ease-in-out-duration $swift-ease-in-out-timing-function;
-  }
   &:not(.md-no-tab-content):not(.md-dynamic-height) {
     min-height: 200 + $tabs-header-height;
   }