Add gyp define to enable vulkan debug layers

include/gpu/vk/GrVkBackendContext.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrVkBackendContext_DEFINED
 #define GrVkBackendContext_DEFINED
 
 #include "SkRefCnt.h"
 
 #include "vk/GrVkDefines.h"
 
-#ifdef SK_DEBUG
-#define ENABLE_VK_LAYERS
-#endif
-
 struct GrVkInterface;
 
 enum GrVkExtensionFlags {
     kEXT_debug_report_GrVkExtensionFlag    = 0x0001,
     kNV_glsl_shader_GrVkExtensionFlag      = 0x0002,
     kKHR_surface_GrVkExtensionFlag         = 0x0004,
     kKHR_swapchain_GrVkExtensionFlag       = 0x0008,
     kKHR_win32_surface_GrVkExtensionFlag   = 0x0010,
     kKHR_android_surface_GrVkExtensionFlag = 0x0020,
     kKHR_xcb_surface_GrVkExtensionFlag     = 0x0040,
@@ skipping 28 matching lines @@
     // Helper function to create the default Vulkan objects needed by the GrVkGpu object
     // If presentQueueIndex is non-NULL, will try to set up presentQueue as part of device
     // creation using the platform-specific canPresent() function.
     static const GrVkBackendContext* Create(uint32_t* presentQueueIndex = nullptr,
                                             CanPresentFn = CanPresentFn());
 
     ~GrVkBackendContext() override;
 };
 
 #endif