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

src/gpu/GrProcOptInfo.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 GrProcOptInfo_DEFINED
 #define GrProcOptInfo_DEFINED
 
 #include "GrColor.h"
 #include "GrInvariantOutput.h"
 
 class GrFragmentStage;
+class GrFragmentProcessor;
 class GrGeometryProcessor;
+class GrProcessor;
 
 /**
  * GrProcOptInfo gathers invariant data from a set of processor stages.It is used to recognize
  * optimizations related to eliminating stages and vertex attributes that aren't necessary for a
  * draw.
  */
 class GrProcOptInfo {
 public:
     GrProcOptInfo()
         : fInOut(0, static_cast<GrColorComponentFlags>(0), false)
         , fFirstEffectStageIndex(0)
         , fInputColorIsUsed(true)
         , fInputColor(0)
         , fRemoveVertexAttrib(false)
-        , fReadsDst(false) {}
+        , fReadsDst(false)
+        , fReadsFragPosition(false) {}
 
     void calcWithInitialValues(const GrFragmentStage*, int stageCount, GrColor startColor,
                                GrColorComponentFlags flags, bool areCoverageStages,
                                const GrGeometryProcessor* gp = NULL);
 
     bool isSolidWhite() const { return fInOut.isSolidWhite(); }
     bool isOpaque() const { return fInOut.isOpaque(); }
     bool isSingleComponent() const { return fInOut.isSingleComponent(); }
 
     GrColor color() const { return fInOut.color(); }
@@ skipping 26 matching lines @@
      * Given the set of optimizations determined by GrProcOptInfo, should the caller remove the
      * color/coverage vertex attribute that was input to the first stage.
      */
     bool removeVertexAttrib() const { return fRemoveVertexAttrib; }
 
     /**
      * Returns true if any of the stages preserved by GrProcOptInfo read the dst color.
      */
     bool readsDst() const { return fReadsDst; }
 
+    /**
+     * Returns true if any of the stages preserved by GrProcOptInfo read the frag position.
+     */
+    bool readsFragPosition() const { return fReadsFragPosition; }
+
 private:
     GrInvariantOutput fInOut;
     int fFirstEffectStageIndex;
     bool fInputColorIsUsed;
     GrColor fInputColor;
     bool fRemoveVertexAttrib;
     bool fReadsDst;
+    bool fReadsFragPosition;
 };
 
 #endif