GitLab

Dispatch the commands in Page domain through an UberDispatcher. Follow up
CLs make this change for the other domains (Browser, Target).

This is in preparation for adding WindowManager domain.

BUG=758061

Change-Id: I35e9dcae13ee9f80e4d81054bdfaf2c5292785ad
Reviewed-on: https://chromium-review.googlesource.com/674263
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504474}