Remove unnecessary setNeedsCompositingUpdate(CompositingUpdateRebuildTree)

The RenderLayerCompositor can determine whether it needs to rebuild the tree.
We don't need to dirty this much state.

R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/450403003

git-svn-id: svn://svn.chromium.org/blink/trunk@180008 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/rendering/RenderLayer.cpp

@@ -1252,9 +1252,6 @@ void RenderLayer::addChild(RenderLayer* child, RenderLayer* beforeChild)
 
     setNeedsCompositingInputsUpdate();
 
-    // FIXME: Why do we need to explicitly set CompositingUpdateRebuildTree?
-    compositor()->setNeedsCompositingUpdate(CompositingUpdateRebuildTree);
-
     if (child->stackingNode()->isNormalFlowOnly())
         m_stackingNode->dirtyNormalFlowList();