Remove Request.Context and expose Request.destination

Request.Context was removed from the Fetch spec, and Request.destination
replaced it. Exposing `destination` will enable some use-cases where
Service Worker code needs to know which resource it is dealing with [1].
This CL exposes that property by default.

Intent-to-ship: https://groups.google.com/a/chromium.org/d/msg/blink-dev/Rb3B-l_Gnzc/VtYII4mWBAAJ

Bug: 520460
Change-Id: I75ad00326f2f1e0a93f25132e9b13bea44ccbf2f

[1] https://github.com/whatwg/fetch/issues/634

Change-Id: I75ad00326f2f1e0a93f25132e9b13bea44ccbf2f
Reviewed-on: https://chromium-review.googlesource.com/844081
Commit-Queue: Yoav Weiss <yoav@yoav.ws>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#527523}
19 files changed