Add define of SK_ENABLE_VK_LAYERS to gn build

BUILD.gn

 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("gn/shared_sources.gni")
 
 declare_args() {
   skia_use_expat = true
   skia_use_fontconfig = is_linux
   skia_use_freetype = is_android || is_fuchsia || is_linux
   skia_use_giflib = !is_fuchsia
   skia_use_libjpeg_turbo = true
   skia_use_libpng = true
   skia_use_libwebp = !is_fuchsia
   skia_use_mesa = false
   skia_use_sfntly = !is_fuchsia
   skia_use_vulkan = is_android && defined(ndk_api) && ndk_api >= 24
   skia_use_zlib = true
 
   skia_enable_android_framework_defines = false
   skia_enable_gpu = true
   skia_enable_tools = !is_fuchsia
+
+  # TODO: Vulkan debug layers should be disabled for all client uses of skia as well.
+  skia_enable_vulkan_debug_layers = !is_fuchsia && is_debug
 }
 
 # Our tools require static linking (they use non-exported symbols) and GPU support (just lazy).
 skia_enable_tools = skia_enable_tools && skia_enable_gpu && !is_component_build
 
 fontmgr_android_enabled = skia_use_expat && skia_use_freetype
 
 skia_public_includes = [
   "include/android",
   "include/c",
@@ skipping 287 matching lines @@
     sources += [ "src/gpu/gl/mac/GrGLCreateNativeInterface_mac.cpp" ]
   } else {
     sources += [ "src/gpu/gl/GrGLCreateNativeInterface_none.cpp" ]
   }
   libs = []
 
   if (skia_use_vulkan) {
     public_defines += [ "SK_VULKAN" ]
     sources += skia_vk_sources
     libs += [ "vulkan" ]
+    if (skia_enable_vulkan_debug_layers) {
+      public_defines += [ "SK_ENABLE_VK_LAYERS" ]
+    }
   }
 }
 
 optional("jpeg") {
   enabled = skia_use_libjpeg_turbo
   public_defines = [ "SK_HAS_JPEG_LIBRARY" ]
 
   deps = [
     "//third_party/libjpeg-turbo:libjpeg",
   ]
@@ skipping 557 matching lines @@
       "tools/get_images_from_skps.cpp",
     ]
     deps = [
       ":flags",
       ":skia",
       "//third_party/jsoncpp",
     ]
     testonly = true
   }
 }