[sync] Add hooks to allow for testing sync credential caching in the presence of strange singleton mode

Sync credential caching is currently broken by strange singleton mode, due to the fact that the metro and desktop directories are collapsed into one.

This patch adds test hooks to CredentialCacheService, to allow for its testing using two side-by-side instances of Desktop Chrome, one using the default desktop user data directory, and the other using what used to be the default metro user data directory.

Note that in order to enable these test hooks, the --enable-sync-credential-caching flag will have to be used. If the flag is not used, there will be no change in behavior, and strange singleton mode will continue to work as designed.

TBR=thakis@chromium.org
BUG=144280

Review URL: https://chromiumcodereview.appspot.com/10867019

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@153105 0039d316-1c4b-4281-b951-d872f2087c98
4 files changed