Prepare ui/compositor for WebLayer type change

ui/compositor/compositor.h

Index: ui/compositor/compositor.h
diff --git a/ui/compositor/compositor.h b/ui/compositor/compositor.h
index f598542ab36e1e0f4be0a9b552eaffea722d6c57..27b8dc370c331be131a4cc7b9883387cc743e4b2 100644
--- a/ui/compositor/compositor.h
+++ b/ui/compositor/compositor.h
@@ -7,6 +7,7 @@
 
 #include "base/hash_tables.h"
 #include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
 #include "third_party/WebKit/Source/Platform/chromium/public/WebLayer.h"
 #include "third_party/WebKit/Source/Platform/chromium/public/WebLayerTreeView.h"
@@ -241,7 +242,11 @@ class COMPOSITOR_EXPORT Compositor
   ObserverList<CompositorObserver> observer_list_;
 
   gfx::AcceleratedWidget widget_;
+#if defined(WEBLAYER_IS_PURE_VIRTUAL)
+  scoped_ptr<WebKit::WebLayer> root_web_layer_;
+#else
   WebKit::WebLayer root_web_layer_;
+#endif
   WebKit::WebLayerTreeView host_;
 
   // This is set to true when the swap buffers has been posted and we're waiting