chromeos: Fix shared linking.

BUG=make chrome fails with GYP_DEFINES='chromeos=1 library=shared_library'
TEST=see BUG

Review URL: http://codereview.chromium.org/5690001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@68748 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/chrome_browser.gypi b/chrome/chrome_browser.gypi
index d0368ada..1857edec 100644
--- a/chrome/chrome_browser.gypi
+++ b/chrome/chrome_browser.gypi
@@ -3482,6 +3482,7 @@
         }],
         ['chromeos==1', {
           'sources!': [
+            'browser/background_mode_manager_linux.cc',
             'browser/password_manager/native_backend_gnome_x.h',
             'browser/password_manager/native_backend_gnome_x.cc',
             'browser/password_manager/native_backend_kwallet_x.h',