Add OpenGL context to Viewer.

src/gpu/vk/GrVkBuffer.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrVkBuffer.h"
 #include "GrVkGpu.h"
 #include "GrVkMemory.h"
@@ skipping 108 matching lines @@
 void GrVkBuffer::vkRelease(const GrVkGpu* gpu) {
     VALIDATE();
     fResource->unref(gpu);
     fResource = nullptr;
     fMapPtr = nullptr;
     VALIDATE();
 }
 
 void GrVkBuffer::vkAbandon() {
     fResource->unrefAndAbandon();
+    fResource = nullptr;
     fMapPtr = nullptr;
     VALIDATE();
 }
 
 void* GrVkBuffer::vkMap(const GrVkGpu* gpu) {
     VALIDATE();
     SkASSERT(!this->vkIsMapped());
 
     if (!fResource->unique()) {
         // in use by the command buffer, so we need to create a new one
@@ skipping 53 matching lines @@
     VK_CALL(gpu, UnmapMemory(gpu->device(), alloc()));
 
     return true;
 }
 
 void GrVkBuffer::validate() const {
     SkASSERT(!fResource || kVertex_Type == fDesc.fType || kIndex_Type == fDesc.fType
              || kCopyRead_Type == fDesc.fType || kCopyWrite_Type == fDesc.fType
              || kUniform_Type == fDesc.fType);
 }