Move GraphicsLayerUpdater::rebuildTree into its own file

Source/core/rendering/compositing/RenderLayerCompositor.cpp

Index: Source/core/rendering/compositing/RenderLayerCompositor.cpp
diff --git a/Source/core/rendering/compositing/RenderLayerCompositor.cpp b/Source/core/rendering/compositing/RenderLayerCompositor.cpp
index cb55062f69ab3230c78a54d638a0344812a68be0..cec9b8f870ced809b69fcdc3400137229c2bd9bb 100644
--- a/Source/core/rendering/compositing/RenderLayerCompositor.cpp
+++ b/Source/core/rendering/compositing/RenderLayerCompositor.cpp
@@ -47,6 +47,7 @@
 #include "core/rendering/compositing/CompositedLayerMapping.h"
 #include "core/rendering/compositing/CompositingLayerAssigner.h"
 #include "core/rendering/compositing/CompositingRequirementsUpdater.h"
+#include "core/rendering/compositing/GraphicsLayerTreeBuilder.h"
 #include "core/rendering/compositing/GraphicsLayerUpdater.h"
 #include "platform/OverscrollTheme.h"
 #include "platform/graphics/GraphicsLayer.h"
@@ -404,8 +405,8 @@ void RenderLayerCompositor::updateIfNeeded()
         // Update the hierarchy of the compositing layers.
         GraphicsLayerVector childList;
         {
-            TRACE_EVENT0("blink_rendering", "GraphicsLayerUpdater::rebuildTree");
-            GraphicsLayerUpdater().rebuildTree(*updateRoot, childList);
+            TRACE_EVENT0("blink_rendering", "GraphicsLayerTreeBuilder::rebuild");
+            GraphicsLayerTreeBuilder().rebuild(*updateRoot, childList);
         }
 
         if (childList.isEmpty())