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Tracing web tests dump tracing events that can contain locations in
scripts. These locations may be source mapped. Resolving such a
location will be asynchronous in the future.

This CL prepares all tracing web tests for asynchronous source
mapping by adding async/await to the necessary places and waiting for
pending live location updates where needed.

The PerformanceTestRunner helpers that will be async in the
future are:

  * forAllEvents (since the callback may be async)
  * printTimelineRecordsWithDetails
  * printTraceEventPropertiesWithDetails
  * walkTimelineEventTree(UnderNode)

Note: One test is disabled for now, as the test passes an async
callback to a test helper that does not support that currently.
This test requires the usual 3-way dance.

Bug: chromium:1032016
Change-Id: I78d18b0aed922a06ab6e89db517a70119cd9ff72
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2064209
Commit-Queue: Simon Zünd <szuend@chromium.org>
Reviewed-by: Mathias Bynens <mathias@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743500}