Add supported_locales attribute to external_extensions.json
This CL supports backward compatibility. If supported_locales is
missing, it is supposed that extension supports all locales.
supported_locales is a list of locale strings. Locale may specify
parent locale like "en", in this case the extension will be
installed for all "en*" locales like "en-US", "en-GB", etc. If
browser locale is changed and installed default extension is not
suitable for new locale it will be uninstalled.
BUG=chromium-os:21211
TEST=ExtensionServiceTest.ExternalPrefProvider
Review URL: http://codereview.chromium.org/
8188008
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@104906 0039d316-1c4b-4281-b951-d872f2087c98