Enable setting deferral state on ResourceDispatcher at request start

Enable setting deferral state on ResourceDispatcher at request start

In https://chromium.googlesource.com/chromium/src/+/f92a1f3b9,
blink's ResourceLoader stopped handling load deferrals,
instead leaving it to WebURLLoaderImpl. However,
WebURLLoaderImpl can't quite do everything it needs to, as
ResourceDispatcher also needs to note that the load is
deferred, and it can't do that until a PendingRequest has
been created. Give ResourceDispatcher a way to immediately
mark a load a deferred on start.

BUG=601706
Review URL: https://codereview.chromium.org/1881023004

Cr-Commit-Position: refs/heads/master@{#388910}
(cherry picked from commit c5a3e99a81bee5f325b81be3d21f5daf1854b572)

Committed: https://chromium.googlesource.com/chromium/src/+/cdb8e78779913eca8c5860c8cb8642752b2b9a83

[Nate Chapin, 2016-04-22 21:04:30]

Description was changed from

==========
Enable setting deferral state on ResourceDispatcher at request start

In https://chromium.googlesource.com/chromium/src/+/f92a1f3b9,
blink's ResourceLoader stopped handling load deferrals,
instead leaving it to WebURLLoaderImpl. However,
WebURLLoaderImpl can't quite do everything it needs to, as
ResourceDispatcher also needs to note that the load is
deferred, and it can't do that until a PendingRequest has
been created. Give ResourceDispatcher a way to immediately
mark a load a deferred on start.

BUG=601706

Review URL: https://codereview.chromium.org/1881023004

Cr-Commit-Position: refs/heads/master@{#388910}
(cherry picked from commit c5a3e99a81bee5f325b81be3d21f5daf1854b572)
==========

to

==========
Enable setting deferral state on ResourceDispatcher at request start

In https://chromium.googlesource.com/chromium/src/+/f92a1f3b9,
blink's ResourceLoader stopped handling load deferrals,
instead leaving it to WebURLLoaderImpl. However,
WebURLLoaderImpl can't quite do everything it needs to, as
ResourceDispatcher also needs to note that the load is
deferred, and it can't do that until a PendingRequest has
been created. Give ResourceDispatcher a way to immediately
mark a load a deferred on start.

BUG=601706

Review URL: https://codereview.chromium.org/1881023004

Cr-Commit-Position: refs/heads/master@{#388910}
(cherry picked from commit c5a3e99a81bee5f325b81be3d21f5daf1854b572)

Committed:
https://chromium.googlesource.com/chromium/src/+/cdb8e78779913eca8c5860c8cb86...
==========

[Nate Chapin, 2016-04-22 21:04:32]

Committed patchset #1 (id:1) manually as
cdb8e78779913eca8c5860c8cb8642752b2b9a83.