Add gyp define to enable vulkan debug layers

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 232 matching lines @@
     VkQueue                                fQueue;    // Must be Graphics queue
 
     // Created by GrVkGpu
     GrVkResourceProvider                   fResourceProvider;
     VkCommandPool                          fCmdPool;
     GrVkPrimaryCommandBuffer*              fCurrentCmdBuffer;
     VkPhysicalDeviceMemoryProperties       fPhysDevMemProps;
 
     SkAutoTDelete<GrVkHeap>                fHeaps[kHeapCount];
 
-#ifdef ENABLE_VK_LAYERS
+#ifdef SK_ENABLE_VK_LAYERS
     // For reporting validation layer errors
     VkDebugReportCallbackEXT               fCallback;
 #endif
 
 #if USE_SKSL
     SkSL::Compiler* fCompiler;
 #else
     // 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;
 #endif
 
     typedef GrGpu INHERITED;
 };
 
 #endif