Fix "unknown argument" message from clang plugin on ChromeOS build.

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 1085 matching lines @@
         },
         'conditions': [
           ['chromeos==1', {
             # TODO(rsleevi): http://crbug.com/123295 - Disabled on ChromeOS
             # for now.
             'clang_chrome_plugins_flags': [
               '<@(clang_chrome_plugins_flags)',
               '-Xclang',
               '-plugin-arg-find-bad-constructs',
               '-Xclang',
-              '-skip-refcounted-dtors'
+              'skip-refcounted-dtors'
             ],
           }, {
             'clang_chrome_plugins_flags': [
               '<@(clang_chrome_plugins_flags)',
             ],
           }],
         ],
       }],
 
       # Set use_ibus to 1 to enable ibus support.
@@ skipping 2000 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',
   },
 }