gn/linux: warnings as errors, turn on Wextra

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")
 if (cpu_arch == "arm") {
   import("//build/config/arm.gni")
 }
 if (is_posix) {
   import("//build/config/gcc/gcc_version.gni")
@@ skipping 454 matching lines @@
     ]
 
   }
 }
 
 # chromium_code ---------------------------------------------------------------
 #
 # Toggles between higher and lower warnings for code that is (or isn't)
 # part of Chromium.
 
-# TODO: -Werror should always be on, independent of chromium_code
-# http://crbug.com/393046
 config("chromium_code") {
   if (is_win) {
     cflags = [
       "/W4",  # Warning level 4.
     ]
   } else {
     cflags = [
       "-Wall",
+      "-Wextra",
 
       # GCC turns on -Wsign-compare for C++ under -Wall, but clang doesn't,
       # so we specify it explicitly.
       # TODO(fischman): remove this if http://llvm.org/PR10448 obsoletes it.
       # http://code.google.com/p/chromium/issues/detail?id=90453
       "-Wsign-compare",
     ]
-    if (!is_linux) {
-      # TODO: Add this unconditionally once linux builds without warnings with
-      # clang in the gn build.
-      cflags += [ "-Werror" ]
-    }
 
     # In Chromium code, we define __STDC_foo_MACROS in order to get the
     # C99 macros on Mac and Linux.
     defines = [
       "__STDC_CONSTANT_MACROS",
       "__STDC_FORMAT_MACROS",
     ]
-
-    # TODO(brettw) this should also be enabled on Linux but some files
-    # currently fail.
-    if (is_mac) {
-      cflags += [ "-Wextra" ]
-    }
   }
 }
 config("no_chromium_code") {
   cflags = []
   cflags_cc = []
   defines = []
 
   if (is_win) {
     cflags += [
       "/W3",  # Warning level 3.
@@ skipping 132 matching lines @@
       "/wd4505",  # Unreferenced local function has been removed.
       "/wd4510",  # Default constructor could not be generated.
       "/wd4512",  # Assignment operator could not be generated.
       "/wd4610",  # Class can never be instantiated, constructor required.
     ]
   } else {
     # Common GCC warning setup.
     cflags = [
       # Enables.
       "-Wendif-labels",  # Weird old-style text after an #endif.
+      "-Werror",  # Warnings as errors.
 
       # Disables.
       "-Wno-missing-field-initializers",  # "struct foo f = {0};"
       "-Wno-unused-parameter",  # Unused function parameters.
     ]
     cflags_cc = []
 
     if (is_mac) {
       cflags += [
         "-Wnewline-eof",
@@ skipping 238 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }