Add option to draw wireframe batch bounds

src/gpu/GrGpu.h

Index: src/gpu/GrGpu.h
diff --git a/src/gpu/GrGpu.h b/src/gpu/GrGpu.h
index aeaa595f8b6988745d3fdcea264de3915035bb8a..174234983206136966844ec7c91018dc43860bc7 100644
--- a/src/gpu/GrGpu.h
+++ b/src/gpu/GrGpu.h
@@ -387,6 +387,8 @@ public:
     // clears target's entire stencil buffer to 0
     virtual void clearStencil(GrRenderTarget* target) = 0;
 
+    // draws an outline rectangle for debugging/visualization purposes.
+    virtual void drawDebugWireRect(GrRenderTarget*, const SkIRect&, GrColor) = 0;
 
     // Determines whether a copy of a texture must be made in order to be compatible with
     // a given GrTextureParams. If so, the width, height and filter used for the copy are