[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/2832473002 .
Cr-Commit-Position: refs/branch-heads/3071@{#48}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed: https://chromium.googlesource.com/chromium/src/+/d4b0c9f58ec981f98342cb8438da1a69bb489a06

[droger, 2017-04-19 13:23:47]

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/2832473002 .
Cr-Commit-Position: refs/branch-heads/3071@{#48}
Cr-Branched-From:
a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed:
https://chromium.googlesource.com/chromium/src/+/d4b0c9f58ec981f98342cb8438da...
==========

[droger, 2017-04-19 13:23:49]

Committed patchset #1 (id:1) manually as
d4b0c9f58ec981f98342cb8438da1a69bb489a06.

[ojan, 2017-04-19 18:22:19]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/2833553002/ by ojan@chromium.org.

The reason for reverting is: Caused compile failures on Mac and Windows Beta
official desktop continuous waterfall.

https://bugs.chromium.org/p/chromium/issues/detail?id=713223.