Add "sample locations" feature to GrProcessor

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 61 matching lines @@
     struct KeyHeader {
         // Set by GrGLShaderBuilder if there are effects that read the fragment position. Otherwise,
         // 0.
         uint8_t                     fFragPosKey;
         // Set to uniquely idenitify any swizzling of the shader's output color(s).
         uint8_t                     fOutputSwizzle;
         uint8_t                     fSnapVerticesToPixelCenters;
         int8_t                      fColorEffectCnt;
         int8_t                      fCoverageEffectCnt;
         uint8_t                     fIgnoresCoverage;
+        // Set to uniquely identify the pipeline's sample pattern, or 0 if the shader does not use
+        // sample locations. (We can probably get away with 8 bits here if we ever need more space.)
+        uint16_t                    fSamplePatternKey;
     };
 
     int numColorEffects() const {
         return this->header().fColorEffectCnt;
     }
 
     int numCoverageEffects() const {
         return this->header().fCoverageEffectCnt;
     }
 
@@ skipping 44 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