Add new debug tool to track hardware layers updates

You can setprop debug.hwui.show_layers_updates true to flash
hw layers in green when they update. This is also a setting
in the Dev. section of the settings app.

Change-Id: Ibe1d63a4f81567dc1d590c9b088d2e7505df8abf
diff --git a/libs/hwui/Caches.h b/libs/hwui/Caches.h
index ad1098c..f4f56d6 100644
--- a/libs/hwui/Caches.h
+++ b/libs/hwui/Caches.h
@@ -236,6 +236,7 @@
 
     // Misc
     GLint maxTextureSize;
+    bool debugLayersUpdates;
 
     TextureCache textureCache;
     LayerCache layerCache;
@@ -267,6 +268,7 @@
     void initFont();
     void initExtensions();
     void initConstraints();
+    void initProperties();
 
     static void eventMarkNull(GLsizei length, const GLchar* marker) { }
     static void startMarkNull(GLsizei length, const GLchar* marker) { }