fixed noisy dlog

BUG=none
TBR=rvargas

Review URL: https://codereview.chromium.org/87913002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237320 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237320
Change CreateDirectoryOperation more multi-parent friendly.

No observable change should happen as of now.
This CL ensures that GetExistingDeepestDirectory() returns
a subpath of |directory_path| regardless of the implementation
of ResourceMetadata::GetFilePath().

BUG=319901

Review URL: https://codereview.chromium.org/87483003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237321 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237321