Improve usage of window rectangles

src/gpu/batches/GrClearBatch.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrClearBatch_DEFINED
 #define GrClearBatch_DEFINED
 
@@ skipping 53 matching lines @@
                         HasAABloat::kNo, IsZeroArea::kNo);
         fRenderTarget.reset(rt);
     }
 
     bool onCombineIfPossible(GrBatch* t, const GrCaps& caps) override {
         // This could be much more complicated. Currently we look at cases where the new clear
         // contains the old clear, or when the new clear is a subset of the old clear and is the
         // same color.
         GrClearBatch* cb = t->cast<GrClearBatch>();
         SkASSERT(cb->fRenderTarget == fRenderTarget);
+        if (!fClip.windowRectsState().cheapEqualTo(cb->fClip.windowRectsState())) {
+            return false;
+        }
         if (cb->contains(this)) {
             fClip = cb->fClip;
             this->replaceBounds(*t);
             fColor = cb->fColor;
             return true;
         } else if (cb->fColor == fColor && this->contains(cb)) {
             return true;
         }
         return false;
     }
@@ skipping 12 matching lines @@
     }
 
     GrFixedClip                                             fClip;
     GrColor                                                 fColor;
     GrPendingIOResource<GrRenderTarget, kWrite_GrIOType>    fRenderTarget;
 
     typedef GrBatch INHERITED;
 };
 
 #endif