Fix regression in GrXferProcessor

src/gpu/GrXferProcessor.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrXferProcessor.h"
 #include "GrProcOptInfo.h"
 #include "gl/GrGLCaps.h"
@@ skipping 49 matching lines @@
 void GrXferProcessor::getBlendInfo(BlendInfo* blendInfo) const {
     blendInfo->reset();
     if (!this->willReadDstColor()) {
         this->onGetBlendInfo(blendInfo);
     }
 }
 
 void GrXferProcessor::getGLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const {
     uint32_t key = this->willReadDstColor() ? 0x1 : 0x0;
     if (key) {
-        if (this->getDstTexture()) {
+        if (const GrTexture* dstTexture = this->getDstTexture()) {
             key |= 0x2;
-        }
-        if (kTopLeft_GrSurfaceOrigin == this->getDstTexture()->origin()) {
-            key |= 0x4;
+            if (kTopLeft_GrSurfaceOrigin == dstTexture->origin()) {
+                key |= 0x4;
+            }
         }
         if (this->readsCoverage()) {
             key |= 0x8;
         }
     }
     b->add32(key);
     this->onGetGLProcessorKey(caps, b);
 }
 
 bool GrXferProcessor::willNeedXferBarrier(const GrRenderTarget* rt,
@@ skipping 121 matching lines @@
     }
 #endif
     return this->onCreateXferProcessor(caps, colorPOI, coveragePOI, dstTexture);
 }
 
 bool GrXPFactory::willNeedDstTexture(const GrCaps& caps, const GrProcOptInfo& colorPOI,
                                     const GrProcOptInfo& coveragePOI) const {
     return (this->willReadDstColor(caps, colorPOI, coveragePOI) 
             && !caps.shaderCaps()->dstReadInShaderSupport());
 }