Overview
========

This CL re-enables separate URLLoaderFactories for extensions.  This is
possible because of AppCache-related fixes described below.  Re-enabling
is done by effectively reverting r599434.

AppCache is important, because it represents the scenarios when
RenderFrameHostImpl::CommitNavigation uses a non-network-bound default
URLLoaderFactory (e.g. in these scenarios the default factory is *not*
created via CreateNetworkServiceDefaultFactoryAndObserve).
A regression test for such scenarios is added in
CrossOriginReadBlockingExtensionTest.ProgrammaticContentScriptVsAppCache

For an overview of separate URLLoaderFactories for extensions, see
https://docs.google.com/document/d/1fuBUmLZj1H319jMkK8waUbf5WdQS0N95J_mWXVzbP7A


Avoiding cloberring of the default factory
==========================================

This CL ensures that the initial injection of a content script doesn't
result in cloberring the default URLLoaderFactory, by making sure
RenderFrameHostImpl::MarkInitiatorsAsRequiringSeparateURLLoaderFactory
is capable of pushing down only the new, initiator-specific factories
(without touching the default factory and/or other, untouched
initiator-specific factories).  This also requires ensuring that
RenderFrameHostImpl::CreateInitiatorSpecificURLLoaderFactories takes
as input the origins that need new factories (instead of using all the
origins that the frame needs initiator-specific factories for).


Handling NetworkService crashes
===============================

By having RenderFrameHostImpl::CreateInitiatorSpecificURLLoaderFactories
call CreateNetworkServiceDefaultFactoryAndObserve instead of
CreateNetworkServiceDefaultFactoryInternal, this CL ensures that a
NetworkService crash is detected when initiator-specific (network-bound)
factories are used (and that the crash is detected even if the default
factory is not network-bound).  This makes sure that content scripts in
the test continue to be able to issue network-bound requests after the
crash.

Additionally, introducing
|recreate_default_url_loader_factory_after_network_service_crash_| field
ensures that if the default factory is not network-bound, then it will
not get cloberred when handling a network service crash.  This helps
ensure that the final AppCache request made by the test is successful.


Bug: 846346
Change-Id: Ie53710d17526c140ef8ee65a41de5d3312bfae5b
Reviewed-on: https://chromium-review.googlesource.com/c/1318082
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606352}