Enable composited iframes on hi-DPI.

BUG=272406

Review URL: https://codereview.chromium.org/25593002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227748 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227748
[Files.app] Update tabindex

Update the tabindex along the way of go/filesapp-tabindex.

BUG=246485
TEST=manully

Review URL: https://codereview.chromium.org/26663002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227749 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227749