Correctly align tab and toolbar backgrounds with the frame background.

Correctly align tab and toolbar backgrounds with the frame background.

This fixes off-by-two/off-by-three errors in vertical positioning for themes
that tried to provide aligned tab/toolbar and frame assets.  Tested with several
such themes, including both themes that did and did not provide a custom
background tab image.

BUG=none
TEST=Apply the "Dots" theme from the webstore and open a restored-mode window; the alignment of the background images in the frame, background tabs, and foreground tab should all match.

Committed: https://crrev.com/4942cf0a5685c6db69ef9f3b94b56bb9a36fa561
Cr-Commit-Position: refs/heads/master@{#358431}

[Peter Kasting, 2015-11-05 20:52:50]

pkasting@chromium.org changed reviewers:
+ sky@chromium.org

[sky, 2015-11-06 16:44:22]

LGTM

[Peter Kasting, 2015-11-06 22:03:46]

The CQ bit was checked by pkasting@chromium.org

[commit-bot: I haz the power, 2015-11-06 22:05:35]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1430553004/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1430553004/20001

[commit-bot: I haz the power, 2015-11-06 22:40:56]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-11-06 22:41:42]

Patchset 2 (id:??) landed as
https://crrev.com/4942cf0a5685c6db69ef9f3b94b56bb9a36fa561
Cr-Commit-Position: refs/heads/master@{#358431}