[Prerender] Restore request priorities when swapped in

[Prerender] Restore request priorities when swapped in

Requests from prerendered contents have a IDLE priority, in order not to slow
down visible pages.
However, when the prerendered contents become visible, the request priorities
were not reset back to their correct values, leading to bad prerendering
performance.

In this CL, the priority management for prerender requests is moved to the
PrerenderResourceThrottle/PrerendereContents.
The original priorities are stored in the throttle, and restored when the
prerender contents swaps in.
A new public function is added to ResourceDispatcherHost to update a request
priority, and its implementation reuses the existing code that updates the image
priorities.

The prerender contents keeps a list of all the network resources that were
started while the prerender is hidden. If this proves to be too large, pruning
the list when responses are received should be doable.

BUG=705955
Review-Url: https://codereview.chromium.org/2807163002
Cr-Commit-Position: refs/heads/master@{#464728}
(cherry picked from commit d3bc6148c7f0d2695ec2ca74652d996e2c4f5a6e)

Review-Url: https://codereview.chromium.org/2826223005 .
Cr-Commit-Position: refs/branch-heads/3071@{#83}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed: https://chromium.googlesource.com/chromium/src/+/9440a43cf4f1526f263f187d0d369e80f8615b35

[droger, 2017-04-20 15:30:16]

The CQ bit was checked by droger@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-04-20 15:30:52]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-04-20 15:30:53]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-04-20 15:30:54]

Dry run: CLs for remote refs other than refs/heads/master must contain
NOTRY=true and NOPRESUBMIT=true in order for the CQ to process them

[droger, 2017-04-20 15:54:08]

Description was changed from

==========
[Prerender] Restore request priorities when swapped in

Requests from prerendered contents have a IDLE priority, in order not to slow
down visible pages.
However, when the prerendered contents become visible, the request priorities
were not reset back to their correct values, leading to bad prerendering
performance.

In this CL, the priority management for prerender requests is moved to the
PrerenderResourceThrottle/PrerendereContents.
The original priorities are stored in the throttle, and restored when the
prerender contents swaps in.
A new public function is added to ResourceDispatcherHost to update a request
priority, and its implementation reuses the existing code that updates the image
priorities.

The prerender contents keeps a list of all the network resources that were
started while the prerender is hidden. If this proves to be too large, pruning
the list when responses are received should be doable.

BUG=705955

Review-Url: https://codereview.chromium.org/2807163002
Cr-Commit-Position: refs/heads/master@{#464728}
(cherry picked from commit d3bc6148c7f0d2695ec2ca74652d996e2c4f5a6e)
==========

to

==========
[Prerender] Restore request priorities when swapped in

Requests from prerendered contents have a IDLE priority, in order not to slow
down visible pages.
However, when the prerendered contents become visible, the request priorities
were not reset back to their correct values, leading to bad prerendering
performance.

In this CL, the priority management for prerender requests is moved to the
PrerenderResourceThrottle/PrerendereContents.
The original priorities are stored in the throttle, and restored when the
prerender contents swaps in.
A new public function is added to ResourceDispatcherHost to update a request
priority, and its implementation reuses the existing code that updates the image
priorities.

The prerender contents keeps a list of all the network resources that were
started while the prerender is hidden. If this proves to be too large, pruning
the list when responses are received should be doable.

BUG=705955

Review-Url: https://codereview.chromium.org/2807163002
Cr-Commit-Position: refs/heads/master@{#464728}
(cherry picked from commit d3bc6148c7f0d2695ec2ca74652d996e2c4f5a6e)

Review-Url: https://codereview.chromium.org/2826223005 .
Cr-Commit-Position: refs/branch-heads/3071@{#83}
Cr-Branched-From:
a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed:
https://chromium.googlesource.com/chromium/src/+/9440a43cf4f1526f263f187d0d36...
==========

[droger, 2017-04-20 15:54:11]

Committed patchset #1 (id:1) manually as
9440a43cf4f1526f263f187d0d369e80f8615b35.