Tune the drag/drop behavior of app launcher for re-order vs dropping in folder by making dropping. Make drop into folder easier and fix some subtle bug in calculating nearest tile for drag_view_ and IsFirstEmptySlot.

BUG=343217
R=xiyuan@chromium.org

Review URL: https://codereview.chromium.org/179553005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253490 0039d316-1c4b-4281-b951-d872f2087c98
Extract volume label from a volume Id.

After migrating to file system per volume, we can't use root.name as the volume label, since it is an empty string (as it is a root of the file system). Therefore, the second part of volumeId is used.

TEST=Tested manually with archives.
BUG=340605

Review URL: https://codereview.chromium.org/180793006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253491 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253491