DevTools: allow emulating accept language, user agent and navigator platform via Emulation domain.

Change-Id: Iac5d986f51b86b5c43b20d9cbf1f742684aa610b
Reviewed-on: https://chromium-review.googlesource.com/1072790
Commit-Queue: Pavel Feldman <pfeldman@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562001}
21 files changed