Respect user_scrollable disabling in pinch-virtual-viewport mode.

Respect user_scrollable disabling in pinch-virtual-viewport mode.

user_scrollable_x/y are used to suppress impl-side scrolling when the
page specifies overflow: hidden.  This has been disabled for a while
because of poor interaction with pinch zoom.  In the new pinch-virtual
model, this works better (outer viewport doesn't scroll so that the user
can't see parts of the page not intended to be seen, but pinch zooming
and moving around still works), so re-enable it when that setting is
active.

Note that I'm also planning to start using this for disabling scrolling
for fullscreen elements.

BUG=322223, 175502, 411072
Committed: https://crrev.com/af915a887e3ec61eb029822ac7577a9198628935
Cr-Commit-Position: refs/heads/master@{#299428}

[aelias_OOO_until_Jul13, 2014-10-07 22:26:01]

aelias@chromium.org changed reviewers:
+ bokan@chromium.org

[aelias_OOO_until_Jul13, 2014-10-07 22:27:43]

Hi bokan@, PTAL.  This is useful for fullscreen video anyway so I thought I'd
fix it now.

[bokan, 2014-10-08 15:24:13]

lgtm, exciting that overflow: hidden will finally work correctly :)

[Rick Byers, 2014-10-08 16:53:45]

On 2014/10/08 15:24:13, bokan wrote:
> lgtm, exciting that overflow: hidden will finally work correctly :)

WOOT!  I've been waiting for this day - thanks for all the hard work to get here
guys!

[aelias_OOO_until_Jul13, 2014-10-08 19:47:02]

The CQ bit was checked by aelias@chromium.org

[commit-bot: I haz the power, 2014-10-08 19:48:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/626403003/20001

[commit-bot: I haz the power, 2014-10-08 20:42:31]

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

[commit-bot: I haz the power, 2014-10-08 20:42:33]

Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)

[aelias_OOO_until_Jul13, 2014-10-14 03:43:33]

The CQ bit was checked by aelias@chromium.org

[commit-bot: I haz the power, 2014-10-14 03:44:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/626403003/20001

[commit-bot: I haz the power, 2014-10-14 04:12:13]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-10-14 04:13:16]

Patchset 2 (id:??) landed as
https://crrev.com/af915a887e3ec61eb029822ac7577a9198628935
Cr-Commit-Position: refs/heads/master@{#299428}