Add "sample locations" feature to GrProcessor

src/gpu/glsl/GrGLSLProgramBuilder.h

Index: src/gpu/glsl/GrGLSLProgramBuilder.h
diff --git a/src/gpu/glsl/GrGLSLProgramBuilder.h b/src/gpu/glsl/GrGLSLProgramBuilder.h
index b8669bf2f6e70699b84937c3ad73d6ff7fe48253..a16c050e455147c1a1dc69de227621a7f96868ae 100644
--- a/src/gpu/glsl/GrGLSLProgramBuilder.h
+++ b/src/gpu/glsl/GrGLSLProgramBuilder.h
@@ -10,6 +10,7 @@
 
 #include "GrGeometryProcessor.h"
 #include "GrGpu.h"
+#include "GrPipeline.h"
 #include "glsl/GrGLSLFragmentShaderBuilder.h"
 #include "glsl/GrGLSLGeometryShaderBuilder.h"
 #include "glsl/GrGLSLPrimitiveProcessor.h"
@@ -39,6 +40,11 @@ public:
     const GrPipeline& pipeline() const { return *fArgs.fPipeline; }
     const GrProgramDesc& desc() const { return *fArgs.fDesc; }
     const GrProgramDesc::KeyHeader& header() const { return fArgs.fDesc->header(); }
+    bool canReadFragmentPosition() const { return this->header().fFragPosKey; }
+    bool canUseSampleLocations() const {
+        SkASSERT(!this->header().fSamplePatternKey || this->pipeline().isHWAntialiasState());
+        return this->header().fSamplePatternKey;
+    }
 
     void appendUniformDecls(GrShaderFlags visibility, SkString*) const;