Bug 1383998 - Increase animation generation if attributes are changed. r=heycam

We have to set mHaveNonAnimationRestyles if we have attributes changed
(note: we increase the animation generation only if mHaveNonAnimationRestyles
is set). Attributes changed may create a new transition, and we use the
animation generation as the order of the transition, so
Element::GetAnimations() can return transitions with correct order.

Besides, I think ContentStateChanged() will not trigger a new
transition, so we don't need to make mHaveNonAnimationRestyles there.

MozReview-Commit-ID: J5XgW8nqeLH

--HG--
extra : rebase_source : 24c4b4364935fc5a4b8437f119cbf93035262684

layout/base/ServoRestyleManager.cpp

@@ -1169,6 +1169,10 @@ ServoRestyleManager::TakeSnapshotForAttributeChange(Element* aElement,
   // cause the style to change.
   IncrementUndisplayedRestyleGeneration();
 
+  // Some other random attribute changes may also affect the transitions,
+  // so we also set this true here.
+  mHaveNonAnimationRestyles = true;
+
   ServoElementSnapshot& snapshot = SnapshotFor(aElement);
   snapshot.AddAttrs(aElement, aNameSpaceID, aAttribute);
 
@@ -1228,6 +1232,10 @@ ServoRestyleManager::AttributeChanged(Element* aElement, int32_t aNameSpaceID,
     // Assuming we need to invalidate cached style in getComputedStyle for
     // undisplayed elements, since we don't know if it is needed.
     IncrementUndisplayedRestyleGeneration();
+
+    // If we change attributes, we have to mark this to be true, so we will
+    // increase the animation generation for the new created transition if any.
+    mHaveNonAnimationRestyles = true;
   }
 }