android: Enable -Wunused-const-variable.

build/common.gypi

 # Copyright (c) 2012 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 3202 matching lines @@
           }],
           ['clang==1 and OS=="android"', {
             # Android uses stlport, whose include/new defines
             # `void  operator delete[](void* ptr) throw();`, which
             # clang's -Wimplicit-exception-spec-mismatch warns about for some
             # reason -- http://llvm.org/PR16638. TODO(thakis): Include stlport
             # via -isystem instead.
             'cflags_cc': [
               '-Wno-implicit-exception-spec-mismatch',
             ],
-            'cflags': [
-              # TODO(hans): Remove once we've cleaned up the warnings.
-              # http://crbug.com/307668
-              '-Wno-unused-const-variable',
-            ],
           }],
           ['clang==1 and clang_use_chrome_plugins==1', {
             'cflags': [
               '<@(clang_chrome_plugins_flags)',
             ],
           }],
           ['clang==1 and clang_load!=""', {
             'cflags': [
               '-Xclang', '-load', '-Xclang', '<(clang_load)',
             ],
@@ skipping 1490 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }