Presentation API: add WebRuntimeFeatures to enable/disable the API.

Presentation API: add WebRuntimeFeatures to enable/disable the API.

In order to allow WebView and other projects to turn off the API if they
can't fully support it.

BUG=521319
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=200651

[mlamouri (slow - plz ping), 2015-08-17 15:17:42]

mlamouri@chromium.org changed reviewers:
+ avayvod@chromium.org, mkwst@chromium.org

[mlamouri (slow - plz ping), 2015-08-17 15:18:35]

mlamouri@chromium.org changed reviewers:
+ dcheng@chromium.org

[mlamouri (slow - plz ping), 2015-08-17 15:18:35]

+dcheng@ in case of you can look at it before mkwst@ who is travelling.

[whywhat, 2015-08-17 15:19:55]

lgtm

[Mike West, 2015-08-17 15:26:04]

LGTM.

[mlamouri (slow - plz ping), 2015-08-17 15:28:47]

The CQ bit was checked by mlamouri@chromium.org

[commit-bot: I haz the power, 2015-08-17 15:28:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1299663002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1299663002/1

[commit-bot: I haz the power, 2015-08-17 16:47:42]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=200651