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When chrome browser is under memory pressure,
TabManager::GetSortedLifecycleUnits is called to return list of tabs
sorted by its reactivation score.

We want to log this event by:
(1) generates (and logs) a query_id for this query.
(2) for each tab, when its reactivation score is calculated, we log its
tab_features (with a random label_id) for this query.
(3) when the tab is later on reactivated or closed, we log the label with
the label_id generated before so that feature-label can be paired.

Please see more details in the bug.

Changes made in this CL:

(1) Extending TabMetricsLogger
chrome/browser/resource_coordinator/tab_metrics_logger.h
chrome/browser/resource_coordinator/tab_metrics_logger.cc
chrome/browser/resource_coordinator/tab_metrics_logger_unittest.cc

Minor change of these functions to also take label_id and query_id as input.
(label_id is passed in as input since it's different per tab, query_id is
saved and set inside TabMetricsLogger since it's the same of all tabs per
discard-query)

(2) Populating the label_id and query_id
chrome/browser/resource_coordinator/tab_activity_watcher.h
chrome/browser/resource_coordinator/tab_activity_watcher.cc
chrome/browser/resource_coordinator/tab_activity_watcher_browsertest.cc

TabActivityWatcher::CalculateReactivationScore and
TabActivityWatcher::WebContentsData::CalculateReactivationScore are extended
to also take also_log_to_ukm as input.

A tab_feature with a random label_id_ is logged whenever
CalculateReactivationScore(true) is called. The same label_id_ is also logged
in LogForegroundedOrClosedMetrics.

We also add logic to block background time feature logging for now.

(3) TabManager changes.
chrome/browser/resource_coordinator/tab_lifecycle_unit.cc
chrome/browser/resource_coordinator/tab_manager.h
chrome/browser/resource_coordinator/tab_manager.cc

These changes are necessary only because
TabManager::GetSortedLifecycleUnits and
TabActivityWatcher::CalculateReactivationScore are called at multiple places.
And we only want to log some of them.

a) TabLifecycleUnitSource::TabLifecycleUnit::GetSortKey is changed back to
   only sort by last_activity_time for now.
b)  is added as private function and
   called inside TabManager::DiscardTabImpl if TabRanker is enabled.
c) CalculateReactivationScore(also_log_to_ukm=true) is called inside
   GetSortedLifecycleUnitsFromTabRanker, which is the only case we log query
   time features.

Bug: 900454

Change-Id: Idc77b0ff6aa3488e10a449dfec6a96d4c61f8da0
Reviewed-on: https://chromium-review.googlesource.com/c/1350445Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Michael Giuffrida <michaelpg@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Reviewed-by: Sébastien Marchand <sebmarchand@chromium.org>
Commit-Queue: Charles . <charleszhao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612070}