Revert of Consolidate GPU buffer implementations

src/gpu/vk/GrVkTransferBuffer.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 GrVkTransferBuffer_DEFINED
 #define GrVkTransferBuffer_DEFINED
 
-#include "GrBuffer.h"
+#include "GrTransferBuffer.h"
 #include "GrVkBuffer.h"
 #include "vk/GrVkInterface.h"
 
 class GrVkGpu;
 
-class GrVkTransferBuffer : public GrBuffer, public GrVkBuffer {
+class GrVkTransferBuffer : public GrTransferBuffer, public GrVkBuffer {
 
 public:
     static GrVkTransferBuffer* Create(GrVkGpu* gpu, size_t size, GrVkBuffer::Type type);
 
 protected:
     void onAbandon() override;
     void onRelease() override;
 
 private:
     GrVkTransferBuffer(GrVkGpu* gpu, const GrVkBuffer::Desc& desc,
                        const GrVkBuffer::Resource* resource);
     void setMemoryBacking(SkTraceMemoryDump* traceMemoryDump,
                           const SkString& dumpName) const override;
 
-    void onMap() override {
+    void* onMap() override {
         if (!this->wasDestroyed()) {
-            this->GrBuffer::fMapPtr = this->vkMap(this->getVkGpu());
+            return this->vkMap(this->getVkGpu());
+        } else {
+            return nullptr;
         }
     }
 
     void onUnmap() override {
         if (!this->wasDestroyed()) {
             this->vkUnmap(this->getVkGpu());
         }
     }
 
-    bool onUpdateData(const void* src, size_t srcSizeInBytes) override {
-        SkFAIL("Not implemented for transfer buffers.");
-        return false;
-    }
-
     GrVkGpu* getVkGpu() const {
         SkASSERT(!this->wasDestroyed());
         return reinterpret_cast<GrVkGpu*>(this->getGpu());
     }
 
-    typedef GrBuffer INHERITED;
+    typedef GrTransferBuffer INHERITED;
 };
 
 #endif