Check for xfer barriers in GrBatch, auto-issue barriers in GrGpu

src/gpu/gl/GrGLGpu.h

Index: src/gpu/gl/GrGLGpu.h
diff --git a/src/gpu/gl/GrGLGpu.h b/src/gpu/gl/GrGLGpu.h
index d247a685fdb860040ba5f4195b83e1da96e4d6a0..5d806a7426435d4881f602f80e67c219f1885717 100644
--- a/src/gpu/gl/GrGLGpu.h
+++ b/src/gpu/gl/GrGLGpu.h
@@ -96,8 +96,6 @@ public:
                      const SkIRect& srcRect,
                      const SkIPoint& dstPoint) override;
 
-    void xferBarrier(GrRenderTarget*, GrXferBarrierType) override;
-
     void buildProgramDesc(GrProgramDesc*,
                           const GrPrimitiveProcessor&,
                           const GrPipeline&,
@@ -118,6 +116,8 @@ private:
     // GrGpu overrides
     void onResetContext(uint32_t resetBits) override;
 
+    void xferBarrier(GrRenderTarget*, GrXferBarrierType) override;
+
     GrTexture* onCreateTexture(const GrSurfaceDesc& desc, GrGpuResource::LifeCycle lifeCycle,
                                const void* srcData, size_t rowBytes) override;
     GrTexture* onCreateCompressedTexture(const GrSurfaceDesc& desc,