[Background Fetch] Stop setting blob data handle

on web_requests. This causes us to crash when converting
FetchAPIRequest mojo type to content::ServiceWorkerFetchRequest
since the latter doesn't currently support request body.

Once we switch to using the mojo type everywhere in content, we
can start setting the blob data handle  again from blink.

Bug: 789854, 774054
Change-Id: Icec9a74b9302fb9731febc5adc30f4153dfb698c
Reviewed-on: https://chromium-review.googlesource.com/1209522
Commit-Queue: Mugdha Lakhani <nator@chromium.org>
Reviewed-by: Rayan Kanso <rayankans@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589184}
2 files changed