Introduce the fallback theme engine that will be used to paint a fallback UI

Introduce the fallback theme engine  that will be used to paint a fallback UI

Most native theme widgets don't support zooming and styling.
So we will use the fallback theme in these cases.

Platform::fallbackThemeEngine(): Added a method that returns the
fallback theme. So we can get both the native theme and the default theme.

TEST=None. No behavior change yet.
BUG=84973
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=150182

[tkent, 2013-04-23 12:22:09]

On 2013/04/23 10:20:04, keishi1 wrote:
> Chromium side change: https://codereview.chromium.org/14424007 

You can't land this CL and the Chromium-side CL safely because they depend on
each other.

The fist step should be to add Platform::defaultThemeEngine() and
WebDefaultThemeEngine.h without any other changes.

[keishi, 2013-05-09 12:54:31]

On 2013/04/23 12:22:09, tkent wrote:
> On 2013/04/23 10:20:04, keishi1 wrote:
> > Chromium side change: https://codereview.chromium.org/14424007 
> 
> You can't land this CL and the Chromium-side CL safely because they depend on
> each other.
> 
> The fist step should be to add Platform::defaultThemeEngine() and
> WebDefaultThemeEngine.h without any other changes.
Done. I will upload the rest to a separate issue.

[tkent, 2013-05-09 20:56:22]

Need to add WebFallbackThemeEngine.h to Platform.gypi.

[keishi, 2013-05-10 02:25:11]

On 2013/05/09 20:56:22, tkent wrote:
> Need to add WebFallbackThemeEngine.h to Platform.gypi.

Done.

[tkent, 2013-05-10 02:27:31]

lgtm
But unfortunately I don't own Platform.gypi.

[keishi, 2013-05-10 02:32:37]

abarth@, could you review the change to Platform.gypi. Thanks.

[jamesr, 2013-05-10 02:54:02]

lgtm

[keishi, 2013-05-10 03:09:38]

On 2013/05/10 02:54:02, jamesr wrote:
> lgtm

Thanks.

[commit-bot: I haz the power, 2013-05-10 03:09:49]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/keishi@chromium.org/14108007/14001

[commit-bot: I haz the power, 2013-05-10 09:26:27]

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

[commit-bot: I haz the power, 2013-05-10 12:13:20]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/keishi@chromium.org/14108007/14001

[commit-bot: I haz the power, 2013-05-10 17:39:19]

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

[commit-bot: I haz the power, 2013-05-13 00:02:53]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/keishi@chromium.org/14108007/14001

[commit-bot: I haz the power, 2013-05-13 00:03:05]

Change committed as 150182