gn/linux: warnings as errors, turn on Wextra

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index b04d6dfe35279fd527035de16bc5e1552b7cd0ea..f5eb6a6799082cd1c75a39bf75fe7a68c3a853ea 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -472,8 +472,6 @@ config("runtime_library") {
 # 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 = [
@@ -482,6 +480,7 @@ config("chromium_code") {
   } else {
     cflags = [
       "-Wall",
+      "-Wextra",
 
       # GCC turns on -Wsign-compare for C++ under -Wall, but clang doesn't,
       # so we specify it explicitly.
@@ -489,11 +488,6 @@ config("chromium_code") {
       # 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.
@@ -501,12 +495,6 @@ config("chromium_code") {
       "__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") {
@@ -659,6 +647,7 @@ config("default_warnings") {
     cflags = [
       # Enables.
       "-Wendif-labels",  # Weird old-style text after an #endif.
+      "-Werror",  # Warnings as errors.
 
       # Disables.
       "-Wno-missing-field-initializers",  # "struct foo f = {0};"