Linux/CrOS/Cast/Android (and Mac with gn): Build chromium_code with -Wextra.

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 3137 matching lines @@
             ],
             'cflags_cc': [
               # Don't warn about hash_map in third-party code.
               '-Wno-deprecated',
             ],
             'cflags': [
               # Don't warn about printf format problems.
               # This is off by default in gcc but on in Ubuntu's gcc(!).
               '-Wno-format',
             ],
-            'cflags_cc!': [
-              # Necessary because llvm.org/PR10448 is WONTFIX (crbug.com/90453).
-              '-Wsign-compare',
-            ]
           }],
           # TODO: Fix all warnings on chromeos too.
           [ 'os_posix==1 and OS!="mac" and OS!="ios" and (clang!=1 or chromeos==1)', {
             'cflags!': [
               '-Werror',
             ],
           }],
           [ 'os_posix==1 and os_bsd!=1 and OS!="mac" and OS!="android"', {
             'cflags': [
               # Don't warn about ignoring the return value from e.g. close().
@@ skipping 544 matching lines @@
         '_FILE_OFFSET_BITS=64',
       ],
     }],
     ['os_posix==1 and OS!="mac" and OS!="ios"', {
       'target_defaults': {
         # Enable -Werror by default, but put it in a variable so it can
         # be disabled in ~/.gyp/include.gypi on the valgrind builders.
         'variables': {
           'werror%': '-Werror',
           'libraries_for_target%': '',
+          'conditions' : [
+            # Enable -Wextra for chromium_code when we control the compiler.
+            ['clang==1', { 'wextra': '-Wextra' }, { 'wextra': '-Wno-extra' }],
+          ],
         },
         'defines': [
           '_FILE_OFFSET_BITS=64',
         ],
         'cflags': [
           '<(werror)',  # See note above about the werror variable.
           '-pthread',
           '-fno-strict-aliasing',  # See http://crbug.com/32204
           '-Wall',
+          '<(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 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.
           # Surprisingly, not covered by -fvisibility=hidden.
           '-fvisibility-inlines-hidden',
-          # GCC turns on -Wsign-compare for C++ under -Wall, but clang doesn't,
-          # so we specify it explicitly.  (llvm.org/PR10448, crbug.com/90453)
-          '-Wsign-compare',
         ],
         'ldflags': [
           '-pthread', '-Wl,-z,noexecstack',
         ],
         'libraries' : [
           '<(libraries_for_target)',
         ],
         'configurations': {
           'Debug_Base': {
             'variables': {
@@ skipping 2660 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',
   },
 }