Enable hidpi download UI

Added support for Hidpi in download UI

BUG=136949
TEST=Manual, see instructions below

Run chrome with --force-device-scale-factor=2 --highlight-missing-2x-resources
Ensure that the file type icon in the download bar shows up red

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=148334

[pkotwicz, 2012-07-12 19:46:31]

To address a couple of the conversation topics we had earlier.
It seems as if we are doing this operation on a separate thread because we do
some pretty heavy OS calls in the Win/Linux/Mac case, not the CrOS case.
After talking to bshe@, it turns out that the significantly more expensive
operation is resource loading not the resize.
In this case, the resource will be managed by the resource bundle, so it will
not be a concern

[oshima, 2012-07-12 20:35:07]

lgtm

[pkotwicz, 2012-07-12 20:52:04]

Ben for OWNERS

[pkotwicz, 2012-07-18 18:06:10]

Ping!

[Nico, 2012-07-25 03:59:12]

owners lgtm

[sky, 2012-07-25 04:43:08]

LGTM

[commit-bot: I haz the power, 2012-07-25 14:01:10]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/pkotwicz@chromium.org/10703173/2001

[commit-bot: I haz the power, 2012-07-25 16:13:15]

Change committed as 148334