Loading Predictor: Do not learn resources that have low priority

Loading Predictor: Do not learn resources that have low priority.
This would in turn prevent loading predictor to preconnect
to origins that host low priority resources.

Low priority is defined based on resource priority.

The behavior change is guarded behind a finch experiment.

Change-Id: I86fc31aaa9f191071b621f46c27f851a6be44d90
Bug: 962693
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1567327
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#671957}
17 files changed