Use texture barriers to read directly from the RT

src/gpu/GrPipelineBuilder.h

Index: src/gpu/GrPipelineBuilder.h
diff --git a/src/gpu/GrPipelineBuilder.h b/src/gpu/GrPipelineBuilder.h
index ae9ca9b067b585795a921241c735833dd4f1aa0f..c6f7b311eac6120c2f2d245e5847a2a27a002141 100644
--- a/src/gpu/GrPipelineBuilder.h
+++ b/src/gpu/GrPipelineBuilder.h
@@ -146,6 +146,13 @@ public:
     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.
      */