Promote RenderLayers that have a transition on opacity, transform, or filter

Source/core/rendering/RenderLayerCompositor.cpp

Index: Source/core/rendering/RenderLayerCompositor.cpp
diff --git a/Source/core/rendering/RenderLayerCompositor.cpp b/Source/core/rendering/RenderLayerCompositor.cpp
index 5086bf0565a519c69586194f462a344dd3a44dc7..69a41418297996e02ac87e14256aed3cc830e00f 100644
--- a/Source/core/rendering/RenderLayerCompositor.cpp
+++ b/Source/core/rendering/RenderLayerCompositor.cpp
@@ -1527,6 +1527,7 @@ bool RenderLayerCompositor::requiresOwnBackingStore(const RenderLayer* layer, co
         || requiresCompositingForFrame(renderer)
         || requiresCompositingForBackfaceVisibilityHidden(renderer)
         || requiresCompositingForAnimation(renderer)
+        || requiresCompositingForTransition(renderer)
         || requiresCompositingForFilters(renderer)
         || requiresCompositingForBlending(renderer)
         || requiresCompositingForPosition(renderer, layer)
@@ -1575,6 +1576,9 @@ CompositingReasons RenderLayerCompositor::directReasonsForCompositing(const Rend
     if (requiresCompositingForAnimation(renderer))
         directReasons |= CompositingReasonAnimation;
 
+    if (requiresCompositingForTransition(renderer))
+        directReasons |= CompositingReasonTransition;
+
     if (requiresCompositingForFilters(renderer))
         directReasons |= CompositingReasonFilters;
 
@@ -1629,6 +1633,9 @@ const char* RenderLayerCompositor::logReasonsForCompositing(const RenderLayer* l
     if (reasons & CompositingReasonAnimation)
         return "animation";
 
+    if (reasons & CompositingReasonTransition)
+        return "transition";
+
     if (reasons & CompositingReasonFilters)
         return "filters";
 
@@ -1842,6 +1849,15 @@ bool RenderLayerCompositor::requiresCompositingForAnimation(RenderObject* render
     return false;
 }
 
+bool RenderLayerCompositor::requiresCompositingForTransition(RenderObject* renderer) const
+{
+    if (!(m_compositingTriggers & ChromeClient::AnimationTrigger))
+        return false;
+
+    return renderer->style()->transitionForProperty(CSSPropertyOpacity)
+        || renderer->style()->transitionForProperty(CSSPropertyWebkitTransform);

[shawnsingh, 2013/05/15 19:24:43]

Would it work to accelerate filter transitions as well?  Seems like we do that
for animations already.

[ajuma, 2013/05/17 17:21:29]

Done.

+}
+
 CompositingReasons RenderLayerCompositor::subtreeReasonsForCompositing(RenderObject* renderer, bool hasCompositedDescendants, bool has3DTransformedDescendants) const
 {
     CompositingReasons subtreeReasons = CompositingReasonNone;