Fix bug when drawing background tabs in incognito windows with custom themes.

Fix bug when drawing background tabs in incognito windows with custom themes.

If a theme provided a replacement frame image, but not a replacement incognito
frame or incognito background tab image, the theme service would synthesize one,
but the tab drawing code would not realize this.  As a result it would cache the
appearance of non-hovered background tabs, leading to visual appearance glitches
since not all those tabs should look the same.

BUG=580677
TEST=Install https://chrome.google.com/webstore/detail/tree-branches/bgdeemcfmmabkdhbnhmkhpadancpkgol?hl=en-US , open an incognito window, open several tabs, and ensure the background tab images line up with the frame and the tab appearance doesn't change abruptly when hovering any such tabs.

Committed: https://crrev.com/65740e3efadf5dad31f11b6d50eb6b63ccb3f2d7
Cr-Commit-Position: refs/heads/master@{#371081}

[Peter Kasting, 2016-01-22 22:02:10]

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

[sky, 2016-01-22 22:23:24]

LGTM

[Peter Kasting, 2016-01-22 22:27:55]

The CQ bit was checked by pkasting@chromium.org

[commit-bot: I haz the power, 2016-01-22 22:30:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1623643002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1623643002/1

[commit-bot: I haz the power, 2016-01-22 23:37:09]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-01-22 23:39:00]

Description was changed from

==========
Fix bug when drawing background tabs in incognito windows with custom themes.

If a theme provided a replacement frame image, but not a replacement incognito
frame or incognito background tab image, the theme service would synthesize one,
but the tab drawing code would not realize this.  As a result it would cache the
appearance of non-hovered background tabs, leading to visual appearance glitches
since not all those tabs should look the same.

BUG=580677
TEST=Install
https://chrome.google.com/webstore/detail/tree-branches/bgdeemcfmmabkdhbnhmkh...
, open an incognito window, open several tabs, and ensure the background tab
images line up with the frame and the tab appearance doesn't change abruptly
when hovering any such tabs.
==========

to

==========
Fix bug when drawing background tabs in incognito windows with custom themes.

If a theme provided a replacement frame image, but not a replacement incognito
frame or incognito background tab image, the theme service would synthesize one,
but the tab drawing code would not realize this.  As a result it would cache the
appearance of non-hovered background tabs, leading to visual appearance glitches
since not all those tabs should look the same.

BUG=580677
TEST=Install
https://chrome.google.com/webstore/detail/tree-branches/bgdeemcfmmabkdhbnhmkh...
, open an incognito window, open several tabs, and ensure the background tab
images line up with the frame and the tab appearance doesn't change abruptly
when hovering any such tabs.

Committed: https://crrev.com/65740e3efadf5dad31f11b6d50eb6b63ccb3f2d7
Cr-Commit-Position: refs/heads/master@{#371081}
==========

[commit-bot: I haz the power, 2016-01-22 23:39:01]

Patchset 1 (id:??) landed as
https://crrev.com/65740e3efadf5dad31f11b6d50eb6b63ccb3f2d7
Cr-Commit-Position: refs/heads/master@{#371081}