Headless: Strip X-DevTools-Emulate-Network-Conditions-Client-Id

This header is added when the DevTools Network domain is active.
It's supposed to be stripped before the fetch is sent down the wire.

BUG=546953, 698905

Review-Url: https://codereview.chromium.org/2748743002
Cr-Commit-Position: refs/heads/master@{#456486}
7 files changed