Add automatic generation of mipmaps to Vulkan

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 93 matching lines @@
                                VkPipelineStageFlags dstStageMask,
                                bool byRegion,
                                VkImageMemoryBarrier* barrier) const;
 
     shaderc_compiler_t shadercCompiler() const {
         return fCompiler;
     }
 
     void finishDrawTarget() override;
 
+    void generateMipmap(GrVkTexture* tex) const;
+
 private:
     GrVkGpu(GrContext* context, const GrContextOptions& options,
             const GrVkBackendContext* backendContext);
 
     void onResetContext(uint32_t resetBits) override {}
 
     GrTexture* onCreateTexture(const GrSurfaceDesc& desc, SkBudgeted budgeted,
                                const SkTArray<GrMipLevel>&) override;
 
     GrTexture* onCreateCompressedTexture(const GrSurfaceDesc& desc, SkBudgeted,
@@ skipping 95 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