Add gyp define to enable vulkan debug layers

infra/bots/recipes/swarm_compile.expected/Build-Win-MSVC-x86_64-Release-Vulkan.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport sys, os\npath = sys.argv[1]\nmode = int(sys.argv[2])\nif not os.path.isdir(path):\n  if os.path.exists(path):\n    print \"%s exists but is not a dir\" % path\n    sys.exit(1)\n  os.makedirs(path, mode)\n",
       "[CUSTOM_C:\\_B_WORK]",
       "511"
     ],
     "name": "makedirs checkout_path",
@@ skipping 83 matching lines @@
       "@@@STEP_LOG_LINE@json.output@    \"role\": \"Build\", @@@",
       "@@@STEP_LOG_LINE@json.output@    \"target_arch\": \"x86_64\"@@@",
       "@@@STEP_LOG_LINE@json.output@  }, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"configuration\": \"Release_x64\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"dm_flags\": [@@@",
       "@@@STEP_LOG_LINE@json.output@    \"--dummy-flags\"@@@",
       "@@@STEP_LOG_LINE@json.output@  ], @@@",
       "@@@STEP_LOG_LINE@json.output@  \"do_perf_steps\": false, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"do_test_steps\": false, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"env\": {@@@",
-      "@@@STEP_LOG_LINE@json.output@    \"GYP_DEFINES\": \"qt_sdk=C:/Qt/4.8.5/ skia_arch_type=x86_64 skia_vulkan=1 skia_warnings_as_errors=1 skia_win_debuggers_path=c:/DbgHelp skia_win_ltcg=0\"@@@",
+      "@@@STEP_LOG_LINE@json.output@    \"GYP_DEFINES\": \"qt_sdk=C:/Qt/4.8.5/ skia_arch_type=x86_64 skia_vulkan=1 skia_vulkan_debug_layers=0 skia_warnings_as_errors=1 skia_win_debuggers_path=c:/DbgHelp skia_win_ltcg=0\"@@@",
       "@@@STEP_LOG_LINE@json.output@  }, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"nanobench_flags\": [@@@",
       "@@@STEP_LOG_LINE@json.output@    \"--dummy-flags\"@@@",
       "@@@STEP_LOG_LINE@json.output@  ], @@@",
       "@@@STEP_LOG_LINE@json.output@  \"upload_dm_results\": true, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"upload_perf_results\": false@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
@@ skipping 13 matching lines @@
     "cmd": [
       "python",
       "make.py",
       "most"
     ],
     "cwd": "[CUSTOM_C:\\_B_WORK]\\skia",
     "env": {
       "BUILDTYPE": "Release_x64",
       "CHROME_HEADLESS": "1",
       "CHROME_PATH": "[SLAVE_BUILD]\\src",
-      "GYP_DEFINES": "qt_sdk=C:/Qt/4.8.5/ skia_arch_type=x86_64 skia_vulkan=1 skia_warnings_as_errors=1 skia_win_debuggers_path=c:/DbgHelp skia_win_ltcg=0",
+      "GYP_DEFINES": "qt_sdk=C:/Qt/4.8.5/ skia_arch_type=x86_64 skia_vulkan=1 skia_vulkan_debug_layers=0 skia_warnings_as_errors=1 skia_win_debuggers_path=c:/DbgHelp skia_win_ltcg=0",
       "PATH": "%(PATH)s;RECIPE_PACKAGE_REPO[depot_tools];RECIPE_PACKAGE_REPO[depot_tools]",
       "SKIA_OUT": "[CUSTOM_C:\\_B_WORK]\\skia\\out\\Build-Win-MSVC-x86_64-Release-Vulkan",
       "VK_SDK_PATH": "[SLAVE_BUILD]\\vulkan_1.0.17.0"
     },
     "name": "build most"
   },
   {
     "cmd": [
       "python",
       "-u",
@@ skipping 47 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@    pass@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]