Files.app: Support item selecting by dragging in the grid view.

This CL adds getHitElements method to the grid view and supports item selecting
by dragging in the grid view.

BUG=247278
TEST=manually

Review URL: https://codereview.chromium.org/26776003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228645 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228645
[FileAPI] Clean up WebFileSystemImpl::openFileSystem

Clean up patch for http://crrev.com/228348
This should be land after blink r159531 roll.

Review URL: https://codereview.chromium.org/27124002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228646 0039d316-1c4b-4281-b951-d872f2087c98
Blink roll 159633:159643

http://build.chromium.org/f/chromium/perf/dashboard/ui/changelog_blink.html?url=/trunk&range=159634:159643&mode=html
TBR=
BUG=

Review URL: https://codereview.chromium.org/27295002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228647 0039d316-1c4b-4281-b951-d872f2087c98
Update .DEPS.git

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228648 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228647
SVN changes up to revision 228648