Current firefox2_importer and firefox3_importer could not import empty folder.
This changelist makes it possible to import initially empty folders.
This patch is contributed by Takashi Toyoshima <toyoshim@google.com>.
Original code review: http://codereview.chromium.org/
6373009/
BUG=25863
TEST=add and fix some tests to unit_tests for firefox2_importer and pass it.
Review URL: http://codereview.chromium.org/
6402003
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@72933 0039d316-1c4b-4281-b951-d872f2087c98