Add gyp define to enable vulkan debug layers

tools/buildbot_spec.py

 #
 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 #
 
 #!/usr/bin/env python
 
 usage = '''
@@ skipping 154 matching lines @@
       builder_dict.get('role') == 'Perf'):
       gyp_defs['skia_dump_stats'] = '1'
 
   # CommandBuffer.
   if builder_dict.get('extra_config') == 'CommandBuffer':
     gyp_defs['skia_command_buffer'] = '1'
 
   # Vulkan.
   if builder_dict.get('extra_config') == 'Vulkan':
     gyp_defs['skia_vulkan'] = '1'
+    gyp_defs['skia_vulkan_debug_layers'] = '0'
 
   return gyp_defs
 
 
 cov_skip.extend([lineno(), lineno() + 1])
 def get_extra_env_vars(builder_dict):
   env = {}
   if builder_dict.get('configuration') == CONFIG_COVERAGE:
     # We have to use Clang 3.6 because earlier versions do not support the
     # compile flags we use and 3.7 and 3.8 hit asserts during compilation.
@@ skipping 222 matching lines @@
   if len(sys.argv) == 2 and sys.argv[1] == 'test':
     self_test()
     sys.exit(0)
 
   if len(sys.argv) != 3:
     print usage
     sys.exit(1)
 
   with open(sys.argv[1], 'w') as out:
     json.dump(get_builder_spec(sys.argv[2]), out)