linux and chromeos: Turn on -Wunused-const-variable.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 04c81e5731ba73b5558435e305ddb9fcb3bee899..26fdfa6d4dd5264ab72421391f58e27eabf62b7f 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -3198,10 +3198,6 @@
               # http://crbug.com/255186
               '-Wno-deprecated-register',
 
-              # TODO(hans): Remove once we've cleaned up the warnings.
-              # http://crbug.com/307668
-              '-Wno-unused-const-variable',
-
               # This warns about auto_ptr<>, used in third-party code.
               '-Wno-deprecated-declarations',
             ],
@@ -3225,6 +3221,13 @@
               '-Wno-implicit-exception-spec-mismatch',
             ],
           }],
+          ['clang==1 and OS!="linux"', {
+            'cflags': [
+              # TODO(hans): Remove once we've cleaned up the warnings.
+              # http://crbug.com/307668
+              '-Wno-unused-const-variable',

[hans, 2013/10/18 21:44:59]

what's this for? CrOS & Android?

+            ],
+          }],
           ['clang==1 and clang_use_chrome_plugins==1', {
             'cflags': [
               '<@(clang_chrome_plugins_flags)',