Refine dual-GPU detection on Mac OS X.

Refine dual-GPU detection on Mac OS X.

Only consider the system to have dual GPUs if one is an Intel GPU and
the other isn't. This avoids problems where recent Mac Pros which
contain dual AMD GPUs are considered to be "dual-GPU". One symptom was
a 300 ms scroll lag on these machines once idle for 10 seconds as
described in https://codereview.chromium.org/1147653002/ .

BUG=380026
Committed: https://crrev.com/521697f5d826185b5e7126466110e72f1da2a26f
Cr-Commit-Position: refs/heads/master@{#330471}

[Ken Russell (switch to Gerrit), 2015-05-19 01:02:58]

kbr@chromium.org changed reviewers:
+ ccameron@chromium.org, zmo@chromium.org

[Ken Russell (switch to Gerrit), 2015-05-19 01:02:59]

zmo, ccameron: please review.

tapted: could you please test this CL on your Mac Pro? Thanks.

[Zhenyao Mo, 2015-05-19 01:09:17]

LGTM

kbr confirmed that on Mac, there haven't been any AMD switchables with a low-end
AMD and a hight-end AMD, so this CL should work.

[Ken Russell (switch to Gerrit), 2015-05-19 01:10:19]

On 2015/05/19 01:09:17, Zhenyao Mo wrote:
> LGTM
> 
> kbr confirmed that on Mac, there haven't been any AMD switchables with a
low-end
> AMD and a hight-end AMD, so this CL should work.

Thanks. I'll wait for feedback from tapted@ before CQ'ing this. (Tested it
locally, though only on a single-GPU Mac.)

[tapted, 2015-05-19 01:17:39]

On 2015/05/19 01:10:19, Ken Russell wrote:
> On 2015/05/19 01:09:17, Zhenyao Mo wrote:
> > LGTM
> > 
> > kbr confirmed that on Mac, there haven't been any AMD switchables with a
> low-end
> > AMD and a hight-end AMD, so this CL should work.
> 
> Thanks. I'll wait for feedback from tapted@ before CQ'ing this. (Tested it
> locally, though only on a single-GPU Mac.)

Nice. I tried the repro a few times -- looks like this does the trick. Thanks!

[Ken Russell (switch to Gerrit), 2015-05-19 01:28:43]

On 2015/05/19 01:17:39, tapted wrote:
> On 2015/05/19 01:10:19, Ken Russell wrote:
> > On 2015/05/19 01:09:17, Zhenyao Mo wrote:
> > > LGTM
> > > 
> > > kbr confirmed that on Mac, there haven't been any AMD switchables with a
> > low-end
> > > AMD and a hight-end AMD, so this CL should work.
> > 
> > Thanks. I'll wait for feedback from tapted@ before CQ'ing this. (Tested it
> > locally, though only on a single-GPU Mac.)
> 
> Nice. I tried the repro a few times -- looks like this does the trick. Thanks!

Fantastic. Thanks for testing.

[Ken Russell (switch to Gerrit), 2015-05-19 01:28:46]

The CQ bit was checked by kbr@chromium.org

[commit-bot: I haz the power, 2015-05-19 01:29:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1144843005/1

[commit-bot: I haz the power, 2015-05-19 03:43:47]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-19 03:45:31]

Patchset 1 (id:??) landed as
https://crrev.com/521697f5d826185b5e7126466110e72f1da2a26f
Cr-Commit-Position: refs/heads/master@{#330471}