Key shader on whether frag pos read is relative to top-left or bottom-left

R=robertphillips@google.com

Review URL: https://codereview.chromium.org/14633007

git-svn-id: http://skia.googlecode.com/svn/trunk@9113 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/gl/GrGLProgramDesc.h b/src/gpu/gl/GrGLProgramDesc.h
index 45714a0..b49cb72 100644
--- a/src/gpu/gl/GrGLProgramDesc.h
+++ b/src/gpu/gl/GrGLProgramDesc.h
@@ -79,7 +79,7 @@
         // (1 - colorRGB) as the secondary output. Only set if dual source blending is supported.
         kSecondaryCoverageISC_CoverageOutput,
         // Combines the coverage, dst, and color as coverage * color + (1 - coverage) * dst. This
-        // can only be set if fDstRead is set.
+        // can only be set if fDstReadKey is non-zero.
         kCombineWithDst_CoverageOutput,
 
         kCoverageOutputCnt
@@ -105,9 +105,12 @@
     bool                     fExperimentalGS;
 #endif
 
-    GrGLShaderBuilder::DstReadKey fDstRead;             // set by GrGLShaderBuilder if there
+    GrGLShaderBuilder::DstReadKey fDstReadKey;          // set by GrGLShaderBuilder if there
                                                         // are effects that must read the dst.
                                                         // Otherwise, 0.
+    GrGLShaderBuilder::FragPosKey fFragPosKey;          // set by GrGLShaderBuilder if there are
+                                                        // effects that read the fragment position.
+                                                        // Otherwise, 0.
 
     // should the FS discard if the coverage is zero (to avoid stencil manipulation)
     SkBool8                     fDiscardIfZeroCoverage;