build/common.gypi

diff --git a/build/common.gypi b/build/common.gypi
index c3bc3dff..cbea957 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -3140,12 +3140,8 @@
         },
         'conditions': [
           [ 'os_posix==1 and OS!="mac" and OS!="ios"', {
-            # We don't want to get warnings from third-party code,
-            # so remove any existing warning-enabling flags like -Wall.
-            'cflags!': [
-              '-Wall',
-              '-Wextra',
-            ],
+            # Remove -Wextra for third-party code.
+            'cflags!': [ '-Wextra' ],
             'cflags_cc': [
               # Don't warn about hash_map in third-party code.
               '-Wno-deprecated',
@@ -3155,10 +3151,11 @@
               # 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',
-            ]
+          }],
+          [ 'os_posix==1 and clang!=1 and OS!="mac" and OS!="ios"', {
+            # When we don't control the compiler, don't use -Wall for
+            # third-party code either.
+            'cflags!': [ '-Wall' ],
           }],
           # TODO: Fix all warnings on chromeos too.
           [ 'os_posix==1 and OS!="mac" and OS!="ios" and (clang!=1 or chromeos==1)', {
@@ -3210,7 +3207,7 @@
 
           [ 'OS=="mac" or OS=="ios"', {
             'xcode_settings': {
-              'WARNING_CFLAGS!': ['-Wall', '-Wextra'],
+              'WARNING_CFLAGS!': ['-Wextra'],
             },
             'conditions': [
               ['buildtype=="Official"', {
@@ -3723,6 +3720,10 @@
         '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',
@@ -3732,6 +3733,7 @@
           '-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.
@@ -3748,9 +3750,6 @@
           # 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',