GitLab

This CL adds support to send ExtensionHostMsg_PostMessage IPC from
worker threads. This allows reply to work targeting a Service
Worker.

Bug: 925927
Test: chrome.runtime.sendMessage can use reply callback.
Change-Id: I2c64992847f0f8746a455941a58841e5f1fea8c5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1506009
Commit-Queue: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638314}