Replace some nullptrs with VK_NULL_HANDLE

src/gpu/vk/GrVkRenderPass.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 GrVkRenderPass_DEFINED
 #define GrVkRenderPass_DEFINED
 
 #include "GrTypes.h"
 
 #include "GrVkResource.h"
 
 #include "vulkan/vulkan.h"
 
 class GrVkGpu;
 class GrVkRenderTarget;
 
 class GrVkRenderPass : public GrVkResource {
 public:
-    GrVkRenderPass() : INHERITED(), fRenderPass(nullptr) {}
+    GrVkRenderPass() : INHERITED(), fRenderPass(VK_NULL_HANDLE) {}
     void initSimple(const GrVkGpu* gpu, const GrVkRenderTarget& target);
 
     struct AttachmentsDescriptor {
         struct AttachmentDesc {
             VkFormat fFormat;
             int fSamples;
             AttachmentDesc() : fFormat(VK_FORMAT_UNDEFINED), fSamples(0) {}
             bool operator==(const AttachmentDesc& right) const {
                 return (fFormat == right.fFormat && fSamples == right.fSamples);
             }
@@ skipping 47 matching lines @@
 
     VkRenderPass          fRenderPass;
     AttachmentFlags       fAttachmentFlags;
     AttachmentsDescriptor fAttachmentsDescriptor;
 
     typedef GrVkResource INHERITED;
 };
 
 GR_MAKE_BITFIELD_OPS(GrVkRenderPass::AttachmentFlags);
 
-#endif
+#endif