Histogram how much time we spend for UI/IO thread hopping during SW startup

Not expecting to see a large value in major cases, but want to see how
much.

Bug: 824858
Change-Id: Ifacdd1d651f6512eb5fad4c45346d579f16eda2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1627271
Reviewed-by: Robert Kaplow (slow) <rkaplow@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663368}
4 files changed