Add Rec709 YUV color space support to GrYUVtoRGBEffect.

Add Rec709 YUV color space support to GrYUVtoRGBEffect.

This change is motivated by a recent switch in how chromium handles
<video> color spaces, making rec709 more commonly used. This will
allow video -> canvas copies to take the fast GPU path when we're using
709, just as we do with 601 and jpeg.

Chromium-side change: https://codereview.chromium.org/1236313002

Committed: https://skia.googlesource.com/skia/+/134003902de13ade7795c5145a59b1e77770f2de

[rileya (GONE FROM CHROMIUM), 2015-07-15 01:30:16]

rileya@chromium.org changed reviewers:
+ bsalomon@chromium.org, sugoi@chromium.org

[reed1, 2015-07-16 18:28:14]

reed@google.com changed reviewers:
+ reed@google.com

[reed1, 2015-07-16 18:28:14]

lgtm

[bsalomon, 2015-07-16 18:31:03]

bsalomon@google.com changed reviewers:
+ bsalomon@google.com

[bsalomon, 2015-07-16 18:31:04]

lgtm

[rileya (GONE FROM CHROMIUM), 2015-07-20 17:27:23]

The CQ bit was checked by rileya@chromium.org

[commit-bot: I haz the power, 2015-07-20 17:27:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1241723005/1

[commit-bot: I haz the power, 2015-07-20 17:31:21]

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

[commit-bot: I haz the power, 2015-07-20 17:31:21]

Try jobs failed on following builders:
  Build-Win-MSVC-x86-Debug-Trybot on client.skia.compile (JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Win-MSVC-x86-D...)
  Build-Win-MSVC-x86_64-Debug-Trybot on client.skia.compile (JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Win-MSVC-x86_6...)

[rileya (GONE FROM CHROMIUM), 2015-07-20 21:48:59]

The CQ bit was checked by rileya@chromium.org

[rileya (GONE FROM CHROMIUM), 2015-07-20 21:48:59]

The patchset sent to the CQ was uploaded after l-g-t-m from bsalomon@google.com,
reed@google.com
Link to the patchset: https://codereview.chromium.org/1241723005/#ps20001
(title: "Tricksy floatses.")

[commit-bot: I haz the power, 2015-07-20 21:49:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1241723005/20001

[commit-bot: I haz the power, 2015-07-20 21:52:38]

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

[commit-bot: I haz the power, 2015-07-20 21:52:38]

Try jobs failed on following builders:
  Build-Win-MSVC-x86_64-Debug-Trybot on client.skia.compile (JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Win-MSVC-x86_6...)

[rileya (GONE FROM CHROMIUM), 2015-07-20 21:56:12]

The CQ bit was checked by rileya@chromium.org

[commit-bot: I haz the power, 2015-07-20 21:56:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1241723005/20001

[commit-bot: I haz the power, 2015-07-20 22:00:07]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/134003902de13ade7795c5145a59b1e77770f2de