Move some work from backend onClear to base class clear

src/gpu/GrDrawTarget.h

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrDrawTarget_DEFINED
 #define GrDrawTarget_DEFINED
 
@@ skipping 253 matching lines @@
     virtual void onDrawPaths(const GrPathProcessor*,
                              const GrPathRange*,
                              const void* indices,
                              PathIndexType,
                              const float transformValues[],
                              PathTransformType,
                              int count,
                              const GrStencilSettings&,
                              const PipelineInfo&) = 0;
 
-    virtual void onClear(const SkIRect* rect, GrColor color, bool canIgnoreRect,
-                         GrRenderTarget* renderTarget) = 0;
+    virtual void onClear(const SkIRect& rect, GrColor color, GrRenderTarget* renderTarget) = 0;
 
     /** The subclass's copy surface implementation. It should assume that any clipping has already
         been performed on the rect and point and that the GrGpu supports the copy. */
     virtual void onCopySurface(GrSurface* dst,
                                GrSurface* src,
                                const SkIRect& srcRect,
                                const SkIPoint& dstPoint) = 0;
 
     // Check to see if this set of draw commands has been sent out
     virtual bool       isIssued(uint32_t drawID) { return true; }
@@ skipping 56 matching lines @@
     bool setupClip(const GrPipelineBuilder&,
                    GrPipelineBuilder::AutoRestoreFragmentProcessorState*,
                    GrPipelineBuilder::AutoRestoreStencil*,
                    GrScissorState* scissorState,
                    const SkRect* devBounds) override;
 
     typedef GrDrawTarget INHERITED;
 };
 
 #endif