[SyncFS] Refine different-file-type non-conflicting sync case

Fix non-conflicting local file/folder addition handling.
For
 - dirty local folder v.s. non-dirty remote file case, and
 - dirty local file v.s. non-dirty remote folder,
we should assume local changes are deletion + addition.
Folder-first policy should not be applied here.

BUG=240165

Review URL: https://codereview.chromium.org/80083003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236547 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236547