android: Deflake EarlyTraceEventTest.

On KitKat and possibly other platforms, EarlyTraceEventTest races
with prenative event tracing. This CL makes the test independent
of other early tracing that might be done outside of the test.

Bug: 930174
Change-Id: If179608ea32d6850bbcbcb27bca1f0ff90689f4d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1596454
Auto-Submit: Matthew Cary <mattcary@chromium.org>
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Commit-Queue: Yaron Friedman <yfriedman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656887}
1 file changed