Move some work from backend onClear to base class clear

src/gpu/GrGpu.h

Index: src/gpu/GrGpu.h
diff --git a/src/gpu/GrGpu.h b/src/gpu/GrGpu.h
index b814abf68879ba243679a83b415c2330b3365aee..77d79d77f34a89af65ed543a67067c8518830296 100644
--- a/src/gpu/GrGpu.h
+++ b/src/gpu/GrGpu.h
@@ -450,8 +450,7 @@ private:
     virtual GrIndexBuffer* onCreateIndexBuffer(size_t size, bool dynamic) = 0;
 
     // overridden by backend-specific derived class to perform the clear.
-    virtual void onClear(GrRenderTarget*, const SkIRect* rect, GrColor color,
-                         bool canIgnoreRect) = 0;
+    virtual void onClear(GrRenderTarget*, const SkIRect* rect, GrColor color) = 0;
 
 
     // Overridden by backend specific classes to perform a clear of the stencil clip bits.  This is