tab-switching: Always measure the tab-switch request delay.

Tab-switch requests that are made through devtools for telemetry tests
are not treated as user-gesture. So this metric can not reported in
telemetry tests. However, the cost of this function is not directly
related to the user-gesture itself. So always report this metric and
associated trace event. This allows this to be measured and monitored
in telemetry tests.

BUG=858944

Change-Id: Ib7112b4939c44af099ecfb751fe108bbe8ecec86
Reviewed-on: https://chromium-review.googlesource.com/1152888
Reviewed-by: Michael Wasserman <msw@chromium.org>
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578659}
1 file changed