Add user_gesture param to WebContentsDelegate::ActivateContents

Add user_gesture param to WebContentsDelegate::ActivateContents

This will be used for https://codereview.chromium.org/1135693006

Depends on:
- https://codereview.chromium.org/1153793003

BUG=470830, 489256, 411702

[johnme, 2015-05-22 16:42:40]

johnme@chromium.org changed reviewers:
+ avi@chromium.org

[johnme, 2015-05-22 16:42:41]

Note to reviewers: I've split up adding the parameter into the 1st patch set and
updating the callers into the 2nd patch set, to make this easier to review.

[johnme, 2015-05-22 17:32:48]

The CQ bit was checked by johnme@chromium.org

[commit-bot: I haz the power, 2015-05-22 17:34:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1153813003/20001

[commit-bot: I haz the power, 2015-05-22 17:34:16]

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

[commit-bot: I haz the power, 2015-05-22 17:34:18]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[johnme, 2015-05-22 18:29:14]

On 2015/05/22 17:34:18, I haz the power - commit-bot wrote:
> No LGTM from a valid reviewer yet. Only full committers are accepted.

Oops, wrong button 8-)

[Avi (use Gerrit), 2015-05-22 21:30:13]

lgtm