Use texture barriers to read directly from the RT

src/gpu/GrPipelineBuilder.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrPipelineBuilder_DEFINED
 #define GrPipelineBuilder_DEFINED
 
@@ skipping 128 matching lines @@
     ////
 
     /**
      * Determines whether multiplying the computed per-pixel color by the pixel's fractional
      * coverage before the blend will give the correct final destination color. In general it
      * will not as coverage is applied after blending.
      */
     bool canTweakAlphaForCoverage() const;
 
     /**
+     * Returns whether blending will be done coherently with draw calls that have been submitted
+     * previously. This is generally true, however some blending extensions require the use of a
+     * barrier.
+     */
+    bool willBlendCoherently(const GrDrawTargetCaps& caps) const;
+
+    /**
      * This function returns true if the render target destination pixel values will be read for
      * blending during draw.
      */
     bool willBlendWithDst(const GrPrimitiveProcessor*) const;
 
     /**
      * Installs a GrXPFactory. This object controls how src color, fractional pixel coverage,
      * and the dst color are blended.
      */
     const GrXPFactory* setXPFactory(const GrXPFactory* xpFactory) {
@@ skipping 275 matching lines @@
     mutable GrProcOptInfo fCoverageProcInfo;
     mutable bool fColorProcInfoValid;
     mutable bool fCoverageProcInfoValid;
     mutable GrColor fColorCache;
     mutable GrColor fCoverageCache;
 
     friend class GrPipeline;
 };
 
 #endif