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 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 {
-        // Set by GrGLShaderBuilder if there are effects that read the fragment position. Otherwise,
-        // 0.
-        uint8_t                     fFragPosKey;
+        // Set to uniquely identify the rt's origin, or 0 if the shader does not require this info.
+        uint8_t                     fSurfaceOriginKey;
+        // Set to uniquely identify the sample pattern, or 0 if the shader doesn't use sample
+        // locations.
+        uint8_t                     fSamplePatternKey;
         // 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;
     };
 
     int numColorEffects() const {
         return this->header().fColorEffectCnt;
@@ skipping 50 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