Add overdraw visualization to the debugger

https://codereview.appspot.com/7267043/



git-svn-id: http://skia.googlecode.com/svn/trunk@7627 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/debugger/SkDebugCanvas.h b/debugger/SkDebugCanvas.h
index 238c5c0..a29fe6a 100644
--- a/debugger/SkDebugCanvas.h
+++ b/debugger/SkDebugCanvas.h
@@ -19,11 +19,16 @@
 class SkDebugCanvas : public SkCanvas {
 public:
     SkDebugCanvas(int width, int height);
-    ~SkDebugCanvas();
+    virtual ~SkDebugCanvas();
 
     void toggleFilter(bool toggle);
 
     /**
+     * Enable or disable overdraw visualization
+     */
+    void setOverdrawViz(bool overdrawViz) { fOverdrawViz = overdrawViz; }
+
+    /**
         Executes all draw calls to the canvas.
         @param canvas  The canvas being drawn to
      */
@@ -213,6 +218,8 @@
     SkMatrix fUserMatrix;
     SkMatrix fMatrix;
     SkIRect fClip;
+    bool fOverdrawViz;
+    SkDrawFilter* fOverdrawFilter;
 
     /**
         Number of unmatched save() calls at any point during a draw.