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This introduces 4 new histograms to add UMA metrics for
Primary ABI Migration.

ag/12863773 is the companion CL on ARC++ side.

Bug: b/170238493
Change-Id: Ib0f970985d728630ec1297a1b38f78f08bec109f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2490673
Commit-Queue: Vaibhav Raheja <vraheja@chromium.org>
Reviewed-by: Josh Horwich <jhorwich@chromium.org>
Reviewed-by: Long Cheng <lgcheng@google.com>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823781}