[SyncFS] Activate the new tracker after UploadNewFile in conflict case

BUG=240165, 325169
R=kinuko@chromium.org, nhiroki@chromium.org

Review URL: https://codereview.chromium.org/102263003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238669 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238669