Prepopulate primary origin's directory database if possible.

Before (with primary origin patch)
140~170 ms

After (excluding 1st launch for a new profile)
30~90 ms

The very first launch for a fresh profile is still slow as
it needs to go through full initialization.

BUG=306030
TEST=manual

Review URL: https://codereview.chromium.org/39823003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230998 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230998