The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0b4c96941d56a85d0fa816ca0e6d079b8581d322

commit 0b4c96941d56a85d0fa816ca0e6d079b8581d322
Author: Sylvain Defresne <sdefresne@chromium.org>
Date: Tue Sep 11 14:10:15 2018

Add histogram to record number of accounts loaded

If the number of accounts known to the AccountTrackerService is
small, then a better data structure could be used instead of a
std::map<std::string, AccountState> to store them.

Add histogram to record the number of accounts loaded from the
preferences by the AccountTrackerService.

Bug:  881250 
Change-Id: I024cf44b4718885a77315813bdb565042fbb6f83
Reviewed-on: https://chromium-review.googlesource.com/1216685
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590292}
[modify] https://crrev.com/0b4c96941d56a85d0fa816ca0e6d079b8581d322/components/signin/core/browser/account_tracker_service.cc
[modify] https://crrev.com/0b4c96941d56a85d0fa816ca0e6d079b8581d322/components/signin/core/browser/account_tracker_service_unittest.cc
[modify] https://crrev.com/0b4c96941d56a85d0fa816ca0e6d079b8581d322/tools/metrics/histograms/histograms.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bf19b2ee93836a9bb047affba0248816c33098c8

commit bf19b2ee93836a9bb047affba0248816c33098c8
Author: Sylvain Defresne <sdefresne@chromium.org>
Date: Tue Sep 11 22:13:07 2018

Add expiration date to Signin.AccountTracker.* histograms

Histograms will be logged starting with M-71, so add an
expiration date of M-76 (five releases or a bit over
six month).

Bug:  881250 
Change-Id: I73fb44340755f3fb1afbf2d01e34c5068dc49da9
Reviewed-on: https://chromium-review.googlesource.com/1219233
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590500}
[modify] https://crrev.com/bf19b2ee93836a9bb047affba0248816c33098c8/tools/metrics/histograms/histograms.xml