Move some work from backend onClear to base class clear

src/gpu/GrImmediateDrawTarget.h

Index: src/gpu/GrImmediateDrawTarget.h
diff --git a/src/gpu/GrImmediateDrawTarget.h b/src/gpu/GrImmediateDrawTarget.h
index b6fda0759998deb8c2e82528bc1f65e65b36bdc5..0fc049e33735ba296f74b0f24ec255bedf742679 100644
--- a/src/gpu/GrImmediateDrawTarget.h
+++ b/src/gpu/GrImmediateDrawTarget.h
@@ -63,9 +63,8 @@ private:
                      const PipelineInfo&) override {
         SkFAIL("Only batch implemented\n");
     }
-    void onClear(const SkIRect* rect,
+    void onClear(const SkIRect& rect,
                  GrColor color,
-                 bool canIgnoreRect,
                  GrRenderTarget* renderTarget) override;
     void onCopySurface(GrSurface* dst,
                        GrSurface* src,