Use texture barriers to read directly from the RT

src/gpu/gl/GrGLGpu.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGLGpu_DEFINED
 #define GrGLGpu_DEFINED
 
@@ skipping 92 matching lines @@
     bool canCopySurface(const GrSurface* dst,
                         const GrSurface* src,
                         const SkIRect& srcRect,
                         const SkIPoint& dstPoint) override;
 
     void buildProgramDesc(GrProgramDesc*,
                           const GrPrimitiveProcessor&,
                           const GrPipeline&,
                           const GrBatchTracker&) const override;
 
+    void blendBarrier() override;
+
 private:
     // GrGpu overrides
     void onResetContext(uint32_t resetBits) override;
 
     GrTexture* onCreateTexture(const GrSurfaceDesc& desc, bool budgeted, const void* srcData,
                                size_t rowBytes) override;
     GrTexture* onCreateCompressedTexture(const GrSurfaceDesc& desc, bool budgeted,
                                          const void* srcData) override;
     GrVertexBuffer* onCreateVertexBuffer(size_t size, bool dynamic) override;
     GrIndexBuffer* onCreateIndexBuffer(size_t size, bool dynamic) override;
@@ skipping 340 matching lines @@
 
     // we record what stencil format worked last time to hopefully exit early
     // from our loop that tries stencil formats and calls check fb status.
     int fLastSuccessfulStencilFmtIdx;
 
     typedef GrGpu INHERITED;
     friend class GrGLPathRendering; // For accessing setTextureUnit.
 };
 
 #endif