Fix scrollbar rendering on Mac 10.6 impl-side painting

Fix scrollbar rendering on Mac 10.6 impl-side painting

The function ScrollbarThemeMacNonOverlayAPI::paint calls into
HIThemeDrawTrack to draw the track alone, then calls into
WebThemeEngineImpl::paintScrollbarThumb (a la Mac), to make
the exact same HIThemeDrawTrack call, just with a thumb added.
Coalesce these into a single call to HIThemeDrawTrack, which
makes the thumb actually appear.

The reason that the thumb wasn't appearing in the first place is
that the nested gfx::SkiaBitLocker instances weren't playing nice
with each other. In non-impl-side painting, the gfx::SkiaBitLocker
instances would draw to the underlying canvas. With impl-side
painting, they were drawn offscreen, and this evidently doesn't
work (tested by passing the CGContextRef directly to the
WebThemeEngineImpl::paintScrollbarThumb call rather than
creating a separate gfx::SkiaBitLocker, not root-caused).

So, the solution is a bit roundabout in the sense that it just
side-steps the gfx::SkiaBitLocker problem, but this is better
than fixing that problem and continuing to do this in the
double-identical-draw-for-no-reason manner.

BUG=409708
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=181499

[ccameron, 2014-09-05 01:49:23]

ccameron@chromium.org changed reviewers:
+ esprehn@chromium.org

[ccameron, 2014-09-05 01:52:11]

Fix for the vanishing scrollbar thumbs.

After this we can murder the WebThemeEngineImpl::paintScrollbarThumb
implementation, cause it will be unused (prepping in
https://codereview.chromium.org/542903002).

[esprehn, 2014-09-05 02:03:13]

lgtm, it's a shame we can't get a test for this, but we'll get that once the
layout tests run with impl side painting.

[esprehn, 2014-09-05 02:03:45]

On 2014/09/05 at 02:03:13, esprehn wrote:
> lgtm, it's a shame we can't get a test for this, but we'll get that once the
layout tests run with impl side painting.

btw, should SkiaBitLocker assert if we nest them since it doesn't work?

[ccameron, 2014-09-05 02:07:28]

On 2014/09/05 02:03:45, esprehn wrote:
> On 2014/09/05 at 02:03:13, esprehn wrote:
> > lgtm, it's a shame we can't get a test for this, but we'll get that once the
> layout tests run with impl side painting.
> 
> btw, should SkiaBitLocker assert if we nest them since it doesn't work?

Thanks! Yes, it probably should -- it lives in the Chromium tree, so I'll have
to attack it there.

[ccameron, 2014-09-05 04:42:54]

The CQ bit was checked by ccameron@chromium.org

[commit-bot: I haz the power, 2014-09-05 04:43:50]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ccameron@chromium.org/544913002/1

[commit-bot: I haz the power, 2014-09-05 06:25:08]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-05 06:25:09]

Try jobs failed on following builders:
  mac_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/22296)

[ccameron, 2014-09-05 17:12:16]

On 2014/09/05 06:25:09, I haz the power (commit-bot) wrote:
> Try jobs failed on following builders:
>   mac_blink_rel on tryserver.blink
>
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/22296)

Elliot, any idea what I can do to see what these failures are -- there are tons,
and (naturally) none of them reproduce locally.

[ccameron, 2014-09-05 17:23:40]

On 2014/09/05 17:12:16, ccameron1 wrote:
> On 2014/09/05 06:25:09, I haz the power (commit-bot) wrote:
> > Try jobs failed on following builders:
> >   mac_blink_rel on tryserver.blink
> >
>
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/22296)
> 
> Elliot, any idea what I can do to see what these failures are -- there are
tons,
> and (naturally) none of them reproduce locally.

(to be more specific -- is there any way to see what the image differences are)?

[esprehn, 2014-09-05 17:25:20]

On 2014/09/05 17:23:40, ccameron1 wrote:
> On 2014/09/05 17:12:16, ccameron1 wrote:
> > On 2014/09/05 06:25:09, I haz the power (commit-bot) wrote:
> > > Try jobs failed on following builders:
> > >   mac_blink_rel on tryserver.blink
> > >
> >
>
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/22296)
> > 
> > Elliot, any idea what I can do to see what these failures are -- there are
> tons,
> > and (naturally) none of them reproduce locally.
> 
> (to be more specific -- is there any way to see what the image differences
are)?

Use the layout test results link from the builder status page:
https://storage.googleapis.com/chromium-layout-test-archives/mac_blink_rel/22...

[esprehn, 2014-09-05 17:27:56]

Looking at some diffs it looks like you shifted the gel pattern slightly in the
scroll thumb.

[ccameron, 2014-09-05 19:23:00]

Thanks -- I pulled this up on a 10.6 machine ... and the new version looks to be
the correct version (it actually knows the state of the rest of the scrollbar
when it draws the thumb, unlike the old call). Is there a better way to handle
this many rebaselines?

[ccameron, 2014-09-05 21:11:54]

The CQ bit was checked by ccameron@chromium.org

[commit-bot: I haz the power, 2014-09-05 21:12:28]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ccameron@chromium.org/544913002/40001

[commit-bot: I haz the power, 2014-09-06 07:36:45]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-06 07:36:46]

Exceeded time limit waiting for builds to trigger.

[esprehn, 2014-09-06 08:58:59]

The CQ bit was checked by esprehn@chromium.org

[commit-bot: I haz the power, 2014-09-06 08:59:51]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ccameron@chromium.org/544913002/40001

[commit-bot: I haz the power, 2014-09-06 11:00:24]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-06 11:00:26]

Exceeded time limit waiting for builds to trigger.

[ccameron, 2014-09-06 16:23:30]

The CQ bit was checked by ccameron@chromium.org

[commit-bot: I haz the power, 2014-09-06 16:24:12]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ccameron@chromium.org/544913002/40001

[commit-bot: I haz the power, 2014-09-06 16:24:48]

Committed patchset #3 (id:40001) as 181499