Make all blending up to GrOptDrawState be handled by the xp/xp factory.

src/gpu/GrProcOptInfo.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrProcOptInfo.h"
 
+#include "GrFragmentProcessor.h"
+#include "GrFragmentStage.h"
 #include "GrGeometryProcessor.h"
-#include "GrFragmentStage.h"
 
 void GrProcOptInfo::calcWithInitialValues(const GrFragmentStage* stages,
                                           int stageCount,
                                           GrColor startColor,
                                           GrColorComponentFlags flags,
                                           bool areCoverageStages,
                                           const GrGeometryProcessor* gp) {
     fInOut.reset(startColor, flags, areCoverageStages);
     fFirstEffectStageIndex = 0;
     fInputColorIsUsed = true;
     fInputColor = startColor;
     fRemoveVertexAttrib = false;
     fReadsDst = false;
+    fReadsFragPosition = false;
 
     if (areCoverageStages && gp) {
         gp->computeInvariantOutput(&fInOut);
     }
 
     for (int i = 0; i < stageCount; ++i) {
         const GrFragmentProcessor* processor = stages[i].getProcessor();
         fInOut.resetWillUseInputColor();
         processor->computeInvariantOutput(&fInOut);
-        #ifdef SK_DEBUG
+#ifdef SK_DEBUG
         fInOut.validate();
-        #endif
+#endif
         if (!fInOut.willUseInputColor()) {
             fFirstEffectStageIndex = i;
             fInputColorIsUsed = false;
-            fReadsDst = false; // Reset this since we don't care if previous stages read dst
+            // Reset these since we don't care if previous stages read these values
+            fReadsDst = false;
+            fReadsFragPosition = false;
         }
         if (processor->willReadDstColor()) {
             fReadsDst = true;
         }
+        if (processor->willReadFragmentPosition()) {
+            fReadsFragPosition = true;
+        }
         if (kRGBA_GrColorComponentFlags == fInOut.validFlags()) {
             fFirstEffectStageIndex = i + 1;
             fInputColor = fInOut.color();
             fInputColorIsUsed = true;
             fRemoveVertexAttrib = true;
             // Since we are clearing all previous color stages we are in a state where we have found
             // zero stages that don't multiply the inputColor.
             fInOut.resetNonMulStageFound();
-            fReadsDst = false; // Reset this since we don't care if previous stages read dst
+            // Reset these since we don't care if previous stages read these values
+            fReadsDst = false;
+            fReadsFragPosition = false;
         }
     }
 }
+