Disable new Clang warning -Wsigned-enum-bitfield

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 1018 matching lines @@
       cflags += [
         # TODO(thakis): https://crbug.com/604888
         "-Wno-undefined-var-template",
 
         # TODO(thakis): https://crbug.com/617318
         "-Wno-nonportable-include-path",
 
         # TODO(hans): https://crbug.com/637306
         "-Wno-address-of-packed-member",
       ]
+      if (llvm_force_head_revision) {
+        cflags += [
+          # TODO(hans): https://crbug.com/666144
+          "-Wno-signed-enum-bitfield",
+        ]
+      }
     }
   }
 }
 
 # chromium_code ---------------------------------------------------------------
 #
 # Toggles between higher and lower warnings for code that is (or isn't)
 # part of Chromium.
 
 config("chromium_code") {
@@ skipping 558 matching lines @@
 
 if (is_ios || is_mac) {
   # On Mac and iOS, this enables support for ARC (automatic ref-counting).
   # See http://clang.llvm.org/docs/AutomaticReferenceCounting.html.
   config("enable_arc") {
     common_flags = [ "-fobjc-arc" ]
     cflags_objc = common_flags
     cflags_objcc = common_flags
   }
 }