Fix navigations in OOP PDF

Fix navigations in OOP PDF

Navigations broke as a result of being inside a browser plugin because the
embedded WebContents would be navigated instead of the top-level one.

This change switches to use the chrome.tabs API to do navigations which
fixes this problem.

BUG=446390
Committed: https://crrev.com/8ba5a02786e485034353eebddb1bd9aee2b69b46
Cr-Commit-Position: refs/heads/master@{#310062}

[raymes, 2015-01-06 06:04:51]

raymes@chromium.org changed reviewers:
+ sammc@chromium.org

[Sam McNally, 2015-01-06 06:15:20]

lgtm

[raymes, 2015-01-06 06:16:05]

The CQ bit was checked by raymes@chromium.org

[commit-bot: I haz the power, 2015-01-06 06:16:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/787223005/1

[commit-bot: I haz the power, 2015-01-06 07:08:13]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-06 07:08:57]

Patchset 1 (id:??) landed as
https://crrev.com/8ba5a02786e485034353eebddb1bd9aee2b69b46
Cr-Commit-Position: refs/heads/master@{#310062}