Remove RootDirectory constant from FileManager class.

Previously FileManager class obtain the volume information of drive by using
RootDirectory.DRIVE constant. This CL changes the behavior to obtain the volume
information by using current directory entry.

BUG=302090
TEST=manually

Review URL: https://codereview.chromium.org/96303002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238030 0039d316-1c4b-4281-b951-d872f2087c98
Delete extra_input_method_instances.

BUG=N/A

Review URL: https://codereview.chromium.org/97783002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238031 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238031