Bug 1031319 part 1 - Don't generate element animations when animation-name is "none"; r=dbaron

This patch causes animations whose corresponding animation-name is "none" to be
dropped from the list of generated ElementAnimation objects. This means we avoid
generating events for these animations.

layout/style/AnimationCommon.h

@@ -375,7 +375,7 @@ public:
   // Return the duration of the active interval for the given timing parameters.
   static mozilla::TimeDuration ActiveDuration(const AnimationTiming& aTiming);
 
-  nsString mName; // empty string for 'none'
+  nsString mName;
   AnimationTiming mTiming;
   // The beginning of the delay period.  This is also set to a null
   // timestamp to mark transitions that have finished and are due to

layout/style/nsAnimationManager.cpp

@@ -394,6 +394,15 @@ nsAnimationManager::BuildAnimations(nsStyleContext* aStyleContext,
   for (uint32_t animIdx = 0, animEnd = disp->mAnimationNameCount;
        animIdx != animEnd; ++animIdx) {
     const StyleAnimation& src = disp->mAnimations[animIdx];
+
+    // CSS Animations with an animation-name of "none" are represented
+    // by StyleAnimations with an empty name. Unlike animations with an empty
+    // keyframes rule, these "none" animations should not generate events
+    // at all so we drop them here.
+    if (src.GetName().IsEmpty()) {
+      continue;
+    }
+
     nsRefPtr<ElementAnimation> dest =
       *aAnimations.AppendElement(new ElementAnimation());