Use transfer buffer for BatchAtlas texture copies

src/gpu/vk/GrVkGpu.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 GrVkGpu_DEFINED
 #define GrVkGpu_DEFINED
 
@@ skipping 135 matching lines @@
                       void* buffer,
                       size_t rowBytes) override;
 
     bool onWritePixels(GrSurface* surface,
                        int left, int top, int width, int height,
                        GrPixelConfig config, const SkTArray<GrMipLevel>&) override;
 
     bool onTransferPixels(GrSurface*,
                           int left, int top, int width, int height,
                           GrPixelConfig config, GrBuffer* transferBuffer,
-                          size_t offset, size_t rowBytes) override { return false; }
+                          size_t offset, size_t rowBytes) override;
 
     void onResolveRenderTarget(GrRenderTarget* target) override {}
 
     sk_sp<GrVkPipelineState> prepareDrawState(const GrPipeline&,
                                               const GrPrimitiveProcessor&,
                                               GrPrimitiveType,
                                               const GrVkRenderPass&);
 
     // Bind vertex and index buffers
     void bindGeometry(const GrPrimitiveProcessor&, const GrNonInstancedMesh&);
@@ skipping 51 matching lines @@
 
     // Shaderc compiler used for compiling glsl in spirv. We only want to create the compiler once
     // since there is significant overhead to the first compile of any compiler.
     shaderc_compiler_t fCompiler;
 
 
     typedef GrGpu INHERITED;
 };
 
 #endif