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This reverts commit c5126022.

Reason for revert: Suspected cause of linux-rel breakage:
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/linux-rel/2129

Original change's description:
> DevTools: Do not start tracing in renderer process explicitly.
> 
> The tracing is now initiated by the browser process. There's no need
> to start it in renderer anymore. TracingStartedInPage event is not
> going to be produced anymore. It has been replaced with TracingStartedInBrowser.
> 
> Change-Id: I9e7759f7f792421d3f32fd21e82066e13a4901dc
> Reviewed-on: https://chromium-review.googlesource.com/1182287
> Commit-Queue: Alexei Filippov <alph@chromium.org>
> Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#584797}

TBR=dgozman@chromium.org,alph@chromium.org

Change-Id: I16a9138a8ab10ac74e032d02f4d4cbea1b173a30
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/1183802Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584819}