[SyncFS] Refine MetadataDatabase::TryNoSideEffectActivation

Handle multiple tracker case / uninitialized tracker case for fixing LocalToRemoteSyncer::CreateFolder.

BUG=240165
R=kinuko@chromium.org, nhiroki@chromium.org

Review URL: https://codereview.chromium.org/106363002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239128 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239128