Enable find-missing-symbols-at-link-time for chromeos builds too.

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 3516 matching lines @@
     }],
     # TODO(jochen): Enable this on chromeos on arm. http://crbug.com/356580
     ['os_posix==1 and disable_fatal_linker_warnings==0 and use_evdev_gestures==0 and (chromeos==0 or target_arch!="arm")', {
       'target_defaults': {
         'ldflags': [
           '-Wl,--fatal-warnings',
         ],
       },
     }],
     # TODO(thakis): Enable this everywhere. http://crbug.com/371125
-    ['(OS=="linux" or OS=="android") and chromeos==0 and asan==0 and tsan==0 and component=="shared_library" and use_ozone!=1 and buildtype!="Official"', {
+    ['(OS=="linux" or OS=="android") and asan==0 and tsan==0 and component=="shared_library" and use_ozone!=1 and buildtype!="Official"', {
       'target_defaults': {
         'ldflags': [
           '-Wl,-z,defs',
         ],
       },
     }],
     ['os_posix==1 and chromeos==0', {
       # Chrome OS enables -fstack-protector-strong via its build wrapper,
       # and we want to avoid overriding this, so stack-protector is only
       # enabled when not building on Chrome OS.
@@ skipping 2306 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',
   },
 }