[SyncFS] Fix repeated sync job on folder creation conflict

 * Add ActivationStatus to handle MetadataDatabase::TryNoSideEffectActivation acculately
 * Handle same-title case of activation failure

BUG=340181, 331988
TEST=unit_tests --gtest_filter='DriveBackendSyncTest.*'
R=kinuko@chromium.org, nhiroki@chromium.org

Review URL: https://codereview.chromium.org/150123003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248671 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248671