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Currently, the TraceConfig JSON object passed to the DevTools method to
start tracing only supports configuration of the Chrome-internal trace
event data source.

This commit provides additional parameters in DevTools:

- base64-encoded serialized protobuf message which takes precedence
  over other parameters,

- backend selection.

In order to handle new parameters, convert
base::trace_event::TraceConfig to perfetto::TraceConfig before passing
it and add support for the new perfettoConfig protocol param.

Add test to handle Command to run new test:
out/Default/content_browsertests --gtest_filter=DevToolsProtocolTest.TracingWithPerfettoConfig

Bug: chromium:1141381, chromium:1141386
Change-Id: I35e436487b2526bb3bf17bac34b9741712fb5319
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2560581
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836082}