Disable -Wextra for all toolchains.

build/common.gypi

 # Copyright (c) 2012 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 3528 matching lines @@
           '<(werror)',  # See note above about the werror variable.
           '-pthread',
           '-fno-strict-aliasing',  # See http://crbug.com/32204
           '-Wall',
           # TODO(evan): turn this back on once all the builds work.
           # '-Wextra',
           # Don't warn about unused function params.  We use those everywhere.
           '-Wno-unused-parameter',
           # Don't warn about the "struct foo f = {0};" initialization pattern.
           '-Wno-missing-field-initializers',
+          # Don't warn if a comparison is always true or always false due to
+          # the limited range of the data type. This would be nice to do, but
+          # unfortunately, 'char' is signed on some toolchains and unsigned on
+          # others. There are downsides to forcing it to be one or the other.
+          # Forcing signed makes ARM builds less performant, and Windows builds
+          # fail if we force unsigned.
+          '-Wno-type-limits',

[Nico, 2014/11/03 20:42:38]

You only want to add this for gcc builds. clang builds are warning-free.

           # Don't export any symbols (for example, to plugins we dlopen()).
           # Note: this is *required* to make some plugins work.
           '-fvisibility=hidden',
           '-pipe',
         ],
         'cflags_cc': [
           '-fno-exceptions',
           '-fno-rtti',
           '-fno-threadsafe-statics',
           # Make inline functions have hidden visiblity by default.
@@ skipping 2322 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }