Mac: Restore the show animation and subpixel AA for extension permissions prompts

Mac: Restore the show animation and subpixel AA for extension permissions prompts

This regressed with the switchover to the 10.10 SDK. Extension prompts
that had permissions text stopped animating when shown, and the
permissions text lost its subpixel antialiasing. It's likely related to
the "Responsive Scrolling" changes that came in with 10.9 and were
disabled when linking to the 10.6 SDK.

Giving the NSScrollView containing the permissions text a layer restores
the show animation. Giving the NSOutlineView inside the NSScrollView an
opaque background restores the subpixel AA.

BUG=521901, 532791
TEST=At https://chrome.google.com/webstore/detail/nmljjlfbnbekmadhbpfpkcminoejelga
click 'Add to Chrome'. The permissions prompt should animate in, and all
the fonts should look smooth on a non-retina screen (particularly the
blue 'Show Details' link).

Committed: https://crrev.com/2866fa64ce3757530621d31558e2c17cd4de69e7
Cr-Commit-Position: refs/heads/master@{#350706}

[tapted, 2015-09-24 04:05:53]

tapted@chromium.org changed reviewers:
+ rsesek@chromium.org

[tapted, 2015-09-24 04:10:43]

Hi Robert, please take a look

[Robert Sesek, 2015-09-24 18:25:41]

LGTM

[tapted, 2015-09-24 23:35:09]

The CQ bit was checked by tapted@chromium.org

[commit-bot: I haz the power, 2015-09-24 23:36:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1362983005/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1362983005/20001

[commit-bot: I haz the power, 2015-09-24 23:46:15]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-09-24 23:47:37]

Patchset 2 (id:??) landed as
https://crrev.com/2866fa64ce3757530621d31558e2c17cd4de69e7
Cr-Commit-Position: refs/heads/master@{#350706}