make alpha read back of bgra/rgba work

src/gpu/GrProgramDesc.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrProgramDesc_DEFINED
 #define GrProgramDesc_DEFINED
 
@@ skipping 52 matching lines @@
         const uint32_t* bKey = b.asKey();
         for (int i = 0; i < l; ++i) {
             if (aKey[i] != bKey[i]) {
                 return aKey[i] < bKey[i] ? true : false;
             }
         }
         return false;
     }
 
     struct KeyHeader {
+        // Used to handle swizzles because of mismatch between GrPixelConfig of the dst and its
+        // actual format.
+        uint8_t                     fSwapDstRedAndAlpha;
         uint8_t                     fFragPosKey;   // set by GrGLShaderBuilder if there are
                                                    // effects that read the fragment position.
                                                    // Otherwise, 0.
         uint8_t                     fSnapVerticesToPixelCenters;
         int8_t                      fColorEffectCnt;
         int8_t                      fCoverageEffectCnt;
         uint8_t                     fIgnoresCoverage;
     };
-    GR_STATIC_ASSERT(sizeof(KeyHeader) == 5);
 
     int numColorEffects() const {
         return this->header().fColorEffectCnt;
     }
 
     int numCoverageEffects() const {
         return this->header().fCoverageEffectCnt;
     }
 
     int numTotalEffects() const { return this->numColorEffects() + this->numCoverageEffects(); }
@@ skipping 43 matching lines @@
     };
 
     SkSTArray<kPreAllocSize, uint8_t, true>& key() { return fKey; }
     const SkSTArray<kPreAllocSize, uint8_t, true>& key() const { return fKey; }
 
 private:
     SkSTArray<kPreAllocSize, uint8_t, true> fKey;
 };
 
 #endif