Don't create a GXPFactory when blend is SrcOver

src/gpu/GrDrawTarget.cpp

 
 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrDrawTarget.h"
 
@@ skipping 413 matching lines @@
 
     if (this->caps()->useDrawInsteadOfClear()) {
         // This works around a driver bug with clear by drawing a rect instead.
         // The driver will ignore a clear if it is the only thing rendered to a
         // target before the target is read.
         if (rect == &rtRect) {
             this->discard(renderTarget);
         }
 
         GrPipelineBuilder pipelineBuilder;
+        pipelineBuilder.setXPFactory(
+            GrPorterDuffXPFactory::Create(SkXfermode::kSrc_Mode))->unref();
         pipelineBuilder.setRenderTarget(renderTarget);
 
         this->drawNonAARect(pipelineBuilder, color, SkMatrix::I(), *rect);
     } else {
         GrBatch* batch = new GrClearBatch(*rect, color, renderTarget);
         this->recordBatch(batch);
         batch->unref();
     }
 }
 
@@ skipping 103 matching lines @@
     }
 
     return true;
 }
 
 void GrDrawTarget::clearStencilClip(const SkIRect& rect, bool insideClip, GrRenderTarget* rt) {
     GrBatch* batch = new GrClearStencilClipBatch(rect, insideClip, rt);
     this->recordBatch(batch);
     batch->unref();
 }