Hard codes ScrollbarThemeGtkOrAura::scrollbarThickness to 15 in layout test mode

Hard codes ScrollbarThemeGtkOrAura::scrollbarThickness to 15 in layout test mode

As part of 333499 the width of scrollbars under windows is going to
honor what the OS says (as it was before aura). For tests the size
needs to be hardcoded (we had been doing this in ScrollbarThemeWin.cpp).

BUG=333499
332937
TEST=none
R=dpranke@chromium.org, jamesr@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=165497

[Dirk Pranke, 2014-01-21 18:51:58]

lgtm

[commit-bot: I haz the power, 2014-01-21 18:52:35]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sky@chromium.org/144173002/40001

[commit-bot: I haz the power, 2014-01-21 19:16:25]

Retried try job too often on blink_presubmit for step(s) presubmit
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=blink_pres...

[commit-bot: I haz the power, 2014-01-21 20:24:20]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sky@chromium.org/144173002/40001

[commit-bot: I haz the power, 2014-01-21 20:44:20]

Retried try job too often on blink_presubmit for step(s) presubmit
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=blink_pres...

[sky, 2014-01-21 20:45:46]

+jamesr as Dirk isn't an OWNER here.

[jamesr, 2014-01-21 20:46:21]

lgtm

[commit-bot: I haz the power, 2014-01-21 20:48:41]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sky@chromium.org/144173002/40001

[commit-bot: I haz the power, 2014-01-21 21:19:24]

Retried try job too often on linux_blink for step(s) blink_platform_unittests,
webkit_lint, webkit_python_tests, webkit_tests, webkit_unit_tests, wtf_unittests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_blin...

[commit-bot: I haz the power, 2014-01-21 21:40:37]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sky@chromium.org/144173002/280001

[commit-bot: I haz the power, 2014-01-21 22:12:51]

Retried try job too often on linux_blink_rel for step(s) webkit_unit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_blin...

[commit-bot: I haz the power, 2014-01-21 23:21:37]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sky@chromium.org/144173002/280001

[sky, 2014-01-22 00:59:06]

Committed patchset #3 manually as r165497 (presubmit successful).