Make WebPrescientNetworking per-frame

This makes per-process batching into per-frame, which means that
the browser side may get more IPC & DNS prefetch requests
*if* a page / the process has many subframes.
On the other hand, it still will be rate-limited at per-frame level,
and if a page is having too many frames it can also put various
resource problems so I'm not expecting that this particular change
would cause new problems.

Bug: 997049
Change-Id: Ib51518efba11859ab672464f8e6c60180f7c860f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1936407
Commit-Queue: Kinuko Yasuda <[email protected]>
Reviewed-by: Yuchen Liu <[email protected]>
Reviewed-by: Alex Ilin <[email protected]>
Reviewed-by: Yutaka Hirano <[email protected]>
Reviewed-by: Matt Menke <[email protected]>
Reviewed-by: Dominic Farolino <[email protected]>
Cr-Commit-Position: refs/heads/master@{#721985}
33 files changed