Remove obsolete SynthesizeScrollGesture method.

Remove obsolete SynthesizeScrollGesture method.

Tidy up after the interface change to Input.synthesizeScrollGesture

Patch 4 of 4 to fix the overly long delay between
each scroll in smoothness.scrolling_tough_ad_cases caused by the render
thread being unresponsive.

Patch 1: https://codereview.chromium.org/1299643004/
Patch 2: https://codereview.chromium.org/1296993002/
Patch 3: https://codereview.chromium.org/1291513004/

BUG=510398
Committed: https://crrev.com/3ea8e7a13495246cb44318c541df3be3945cacc3
Cr-Commit-Position: refs/heads/master@{#346624}

[alex clarke (OOO till 29th), 2015-08-17 16:09:36]

alexclarke@chromium.org changed reviewers:
+ skyostil@chromium.org

[Sami, 2015-08-17 16:41:38]

That's a funny looking diff. Non-owner lgtm.

[alex clarke (OOO till 29th), 2015-08-17 16:43:16]

alexclarke@chromium.org changed reviewers:
+ pfeldman@chromium.org

[pfeldman, 2015-08-17 17:42:59]

lgtm

[alex clarke (OOO till 29th), 2015-09-01 10:16:45]

The CQ bit was checked by alexclarke@chromium.org

[commit-bot: I haz the power, 2015-09-01 10:16:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1285133008/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1285133008/1

[commit-bot: I haz the power, 2015-09-01 11:10:57]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-01 11:11:43]

Patchset 1 (id:??) landed as
https://crrev.com/3ea8e7a13495246cb44318c541df3be3945cacc3
Cr-Commit-Position: refs/heads/master@{#346624}