[content shell] enable touch events for layout tests

[content shell] enable touch events for layout tests

Also add the touchDragDropEnabled setting to webpreferences.
This will make fast/events/touch tests pass.

BUG=111316
R=tony@chromium.org,creis@chromium.org
TEST=touch tests pass

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=184242

[jochen (gone - plz use gerrit), 2013-02-21 14:58:05]

Tony, please review everything
Charlie, please OWNER stamp the IPC macro change in content/public/common

[tony, 2013-02-21 18:38:37]

LGTM.  Which layout tests does this fix?

[Charlie Reis, 2013-02-22 07:03:05]

LGTM.

[jochen (gone - plz use gerrit), 2013-02-22 21:14:56]

this will make fast/events/touch tests pass

[commit-bot: I haz the power, 2013-02-22 21:16:17]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jochen@chromium.org/12314032/1

[commit-bot: I haz the power, 2013-02-23 00:43:05]

Commit queue rejected this change because the description was changed
between the time the change entered the commit queue and the time it
was ready to commit. You can safely check the commit box again.

[tony, 2013-02-23 00:56:44]

On 2013/02/23 00:43:05, I haz the power (commit-bot) wrote:
> Commit queue rejected this change because the description was changed
> between the time the change entered the commit queue and the time it
> was ready to commit. You can safely check the commit box again.

Sorry, that was my fault.  Setting cq+ again.

[commit-bot: I haz the power, 2013-02-23 00:57:09]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jochen@chromium.org/12314032/1

[commit-bot: I haz the power, 2013-02-23 01:07:38]

Change committed as 184242