Reduce compositing update in Silk's toggle_drawer by 20%

Source/core/rendering/compositing/CompositedLayerMapping.cpp

Index: Source/core/rendering/compositing/CompositedLayerMapping.cpp
diff --git a/Source/core/rendering/compositing/CompositedLayerMapping.cpp b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
index 40ac4ccd786e97b347b483b5e452952a34cc831b..a9e9e1caf2cbdcb7af24e4ea27a292b594c1f8bd 100644
--- a/Source/core/rendering/compositing/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
@@ -421,7 +421,7 @@ void CompositedLayerMapping::updateAfterLayout(UpdateAfterLayoutFlags flags)
         layerCompositor->updateCompositingDescendantGeometry(m_owningLayer->stackingNode(), m_owningLayer, flags & CompositingChildrenOnly);
 
         if (flags & IsUpdateRoot) {
-            updateGraphicsLayerGeometry();
+            updateGraphicsLayerGeometry(GraphicsLayerUpdater::ForceUpdate);
             layerCompositor->updateRootLayerPosition();
             RenderLayerStackingNode* stackingContainer = m_owningLayer->stackingNode()->enclosingStackingContainerNode();
             if (!layerCompositor->compositingLayersNeedRebuild() && stackingContainer && (stackingContainer != m_owningLayer->stackingNode()))
@@ -617,11 +617,17 @@ void CompositedLayerMapping::updateSquashingLayerGeometry(const IntPoint& delta)
     }
 }
 
-void CompositedLayerMapping::updateGraphicsLayerGeometry()
+GraphicsLayerUpdater::UpdateType CompositedLayerMapping::updateGraphicsLayerGeometry(GraphicsLayerUpdater::UpdateType updateType)
 {
     // If we haven't built z-order lists yet, wait until later.
     if (m_owningLayer->stackingNode()->isStackingContainer() && m_owningLayer->stackingNode()->zOrderListsDirty())
-        return;
+        return updateType;
+
+    if (!m_needToUpdateGeometry && updateType != GraphicsLayerUpdater::ForceUpdate)
+        return updateType;
+    m_needToUpdateGeometry = false;
+    if (m_needToUpdateGeometryOfAllDecendants)
+        updateType = GraphicsLayerUpdater::ForceUpdate;
 
     // Set transform property, if it is not animating. We have to do this here because the transform
     // is affected by the layer dimensions.
@@ -781,7 +787,7 @@ void CompositedLayerMapping::updateGraphicsLayerGeometry()
 
     if (m_owningLayer->reflectionInfo() && m_owningLayer->reflectionInfo()->reflectionLayer()->hasCompositedLayerMapping()) {
         CompositedLayerMappingPtr reflectionCompositedLayerMapping = m_owningLayer->reflectionInfo()->reflectionLayer()->compositedLayerMapping();
-        reflectionCompositedLayerMapping->updateGraphicsLayerGeometry();
+        reflectionCompositedLayerMapping->updateGraphicsLayerGeometry(GraphicsLayerUpdater::ForceUpdate);
 
         // The reflection layer has the bounds of m_owningLayer->reflectionLayer(),
         // but the reflected layer is the bounds of this layer, so we need to position it appropriately.
@@ -860,6 +866,8 @@ void CompositedLayerMapping::updateGraphicsLayerGeometry()
     registerScrollingLayers();
 
     updateCompositingReasons();
+
+    return updateType;
 }
 
 void CompositedLayerMapping::registerScrollingLayers()
@@ -1792,6 +1800,23 @@ void CompositedLayerMapping::setBlendMode(blink::WebBlendMode blendMode)
     }
 }
 
+void CompositedLayerMapping::setNeedsGeometryUpdate()
+{
+    m_needToUpdateGeometryOfAllDecendants = true;
+
+    for (RenderLayer* current = m_owningLayer; current; current = current->ancestorCompositingLayer()) {
+        ASSERT(current->hasCompositedLayerMapping());
+        CompositedLayerMappingPtr mapping = current->compositedLayerMapping();
+        mapping->m_needToUpdateGeometry = true;
+    }
+}
+
+void CompositedLayerMapping::willUpdateGeometryOfAllDecendants()
+{
+    ASSERT(!m_needToUpdateGeometry);
+    m_needToUpdateGeometryOfAllDecendants = false;
+}
+
 struct SetContentsNeedsDisplayFunctor {
     void operator() (GraphicsLayer* layer) const
     {