Rewrote BlobReader to not do any kind of network requests.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cb02821074ba14de3d6a503ef204b694b25017a4

commit cb02821074ba14de3d6a503ef204b694b25017a4
Author: Matt Menke <mmenke@chromium.org>
Date: Tue Jun 19 15:40:30 2018

Annotate many of the browser_tests disabled under the NetworkService.

Also remove a couple that either no longer exist, have been disabled
generally due to flakiness, or are now passing.

BUG= 844950 ,  844951 ,  844952 ,  853251 ,  844928 ,
BUG= 843205 ,  844949 ,  844925 ,  844939 , 821021,
BUG=853798,  844973 ,  844927 ,  844926 ,  844950 

Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: I094a012fe2076c7badf86a094140c7d74db183be
Reviewed-on: https://chromium-review.googlesource.com/1104802
Commit-Queue: Matt Menke <mmenke@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568464}
[modify] https://crrev.com/cb02821074ba14de3d6a503ef204b694b25017a4/testing/buildbot/filters/mojo.fyi.network_browser_tests.filter

 Issue 840414  has been merged into this issue.