extensions: Avoid using WebString in Dispatcher::Dispatcher()

extensions: Avoid using WebString in Dispatcher::Dispatcher()

We can't use Blink public APIs in the constructor of Dispatcher because
Blink is not initialized when we create Dispatcher. See [1] for details.

[1] https://codereview.chromium.org/1182083006/

BUG=501171
Committed: https://crrev.com/52ccbf1153a4ce91ac5600413ace937174eba02c
Cr-Commit-Position: refs/heads/master@{#347809}

[bashi, 2015-09-08 00:47:35]

bashi@chromium.org changed reviewers:
+ kalman@chromium.org

[bashi, 2015-09-08 00:47:35]

PTAL?

[not at google - send to devlin, 2015-09-08 16:17:46]

lgtm

[bashi, 2015-09-08 21:41:00]

The CQ bit was checked by bashi@chromium.org

[commit-bot: I haz the power, 2015-09-08 21:41:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1309843013/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1309843013/1

[commit-bot: I haz the power, 2015-09-08 22:20:36]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-08 22:21:14]

Patchset 1 (id:??) landed as
https://crrev.com/52ccbf1153a4ce91ac5600413ace937174eba02c
Cr-Commit-Position: refs/heads/master@{#347809}