Disable -Wextra for all toolchains.

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 511 matching lines @@
 # part of Chromium.
 
 config("chromium_code") {
   if (is_win) {
     cflags = [
       "/W4",  # Warning level 4.
     ]
   } else {
     cflags = [
       "-Wall",
       "-Wextra",

[Nico, 2014/11/03 18:58:42]

I'd just remove this. -Wextra is a no-op in clang, and it's removed on all
non-clang platforms in gyp:
https://code.google.com/p/chromium/codesearch#chromium/src/build/common.gypi&...

 
       # 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",
     ]
 
     # In Chromium code, we define __STDC_foo_MACROS in order to get the
     # C99 macros on Mac and Linux.
@@ skipping 193 matching lines @@
         # which we no longer use. Check if it makes sense to remove
         # this as well. http://crbug.com/316352
         "-Wno-unneeded-internal-declaration",
 
         # TODO(thakis): Remove, http://crbug.com/263960
         "-Wno-reserved-user-defined-literal",
 
         # TODO(hans): Clean this up. Or disable with finer granularity.
         "-Wno-unused-local-typedef",
       ]
+    } else {
+      cflags += [
+        # This warns if a comparison is always true or always false due to
+        # the limited range of the data type, but do not warn for constant
+        # expressions.
+        # Unfortunately, 'char' is signed on some toolchains and unsigned on
+        # others, and 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",
+      ]
     }
     if (gcc_version >= 48) {
       cflags_cc += [
         # See comment for -Wno-c++11-narrowing.
         "-Wno-narrowing",
         # TODO(thakis): Remove, http://crbug.com/263960
         "-Wno-literal-suffix",
       ]
     }
 
@@ skipping 196 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }