ui: Enable debug borders for the UI compositor through layer tree settings.

ui/compositor/layer.h

Index: ui/compositor/layer.h
diff --git a/ui/compositor/layer.h b/ui/compositor/layer.h
index d8ae96662476aa27e3a27b8309cecee6885c4395..51f1cf3eb787602b6b486f3b5587ecc7dc52f92a 100644
--- a/ui/compositor/layer.h
+++ b/ui/compositor/layer.h
@@ -329,7 +329,6 @@ class COMPOSITOR_EXPORT Layer
   void CreateWebLayer();
   void RecomputeTransform();
   void RecomputeDrawsContentAndUVRect();
-  void RecomputeDebugBorderColor();
 
   // Set all filters which got applied to the layer.
   void SetLayerFilters();
@@ -393,7 +392,6 @@ class COMPOSITOR_EXPORT Layer
   scoped_ptr<WebKit::WebSolidColorLayer> solid_color_layer_;
   WebKit::WebLayer* web_layer_;
   bool web_layer_is_accelerated_;
-  bool show_debug_borders_;
 
   // If true, the layer scales the canvas and the texture with the device scale
   // factor as appropriate. When true, the texture size is in DIP.