Add support for a new developer setting: overdraw debugging

Change-Id: I350ba4486577c3289f82c20938f7a35138778727
diff --git a/libs/hwui/OpenGLRenderer.h b/libs/hwui/OpenGLRenderer.h
index 3e34336..43ef9df 100644
--- a/libs/hwui/OpenGLRenderer.h
+++ b/libs/hwui/OpenGLRenderer.h
@@ -739,6 +739,9 @@
      */
     void drawRegionRects(const Region& region);
 
+    void debugOverdraw(bool enable, bool clear);
+    void renderOverdraw();
+
     /**
      * Should be invoked every time the glScissor is modified.
      */