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This CL adds a new metric that records profile switching (incl. window
switching for concurrently open profiles) into metrics.

The CL renames some variables in the activity recorder to keep the code
clear.

Bug: 1121944
Change-Id: Ia9b7fffb022f8013e4eeb4f94c8187dab16e57b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2377712
Commit-Queue: Jan Krcal <jkrcal@chromium.org>
Commit-Queue: Alex Ilin <alexilin@chromium.org>
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Auto-Submit: Jan Krcal <jkrcal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#802183}