Replace WTF::Optional the base::Optional implementation.

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 896 matching lines @@
     if (!is_clang) {
       cflags_cc += [
         # See comment for -Wno-c++11-narrowing.
         "-Wno-narrowing",
       ]
 
       # Don't warn about the "typedef 'foo' locally defined but not used"
       # for gcc 4.8.
       # TODO: remove this flag once all builds work. See crbug.com/227506
       cflags += [ "-Wno-unused-local-typedefs" ]
+
+      # Don't warn about "maybe" uninitialized. Clang doesn't include this
+      # in -Wall but gcc does, and it gives false positives.
+      cflags += [ "-Wno-maybe-uninitialized" ]
     }
   }
 
   # Common Clang and GCC warning setup.
   if (!is_win || is_clang) {
     cflags += [
       # Disables.
       "-Wno-missing-field-initializers",  # "struct foo f = {0};"
       "-Wno-unused-parameter",  # Unused function parameters.
     ]
@@ skipping 500 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
   }
 }