GitLab

- Added GetAllAwContent method in AwContentsLifecycleNotifier
- Changed AwContentsLifecycleNotifier to store AwContents pointer.
- Added AwPageLoadMetricsProvider which uses GetAllAwContent.

Bug: 1072770
Change-Id: Ief07426218df2ca28249de66bba2147f0a64a403
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2158914Reviewed-by: Bo <boliu@chromium.org>
Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Commit-Queue: Tao Bai <michaelbai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#761966}