The b/67748179 has been approved some time ago. Will update this bug once we can land the related webview shell code (as it requires Android SDK roll in chromium)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4d614fbc4aa7f2c0d510b937073129aef76b99a9

commit 4d614fbc4aa7f2c0d510b937073129aef76b99a9
Author: Tim Volodine <timvolodine@chromium.org>
Date: Thu Aug 02 18:44:18 2018

[SystemWebViewShell] Add WebViewTracingActivity for Tracing API telemetry.

Add activity to measure Tracing API related timings. In particular it allows
to measure time for loading a given URL with or without tracing enabled. It
also provides the overall tracing time, i.e. time it takes from starting
tracing until completion when all traces are written to disk.

Example usage:
$ adb shell am start -n org.chromium.webview_shell/.WebViewTracingActivity -a VIEW -d \
  http://www.google.com --ez enableTracing true

BUG= 797312 

Change-Id: Iac5e871952d356762f351527b6aafdb4faf07255
Reviewed-on: https://chromium-review.googlesource.com/1153249
Commit-Queue: Tim Volodine <timvolodine@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580267}
[modify] https://crrev.com/4d614fbc4aa7f2c0d510b937073129aef76b99a9/android_webview/tools/system_webview_shell/BUILD.gn
[modify] https://crrev.com/4d614fbc4aa7f2c0d510b937073129aef76b99a9/android_webview/tools/system_webview_shell/apk/AndroidManifest.xml
[add] https://crrev.com/4d614fbc4aa7f2c0d510b937073129aef76b99a9/android_webview/tools/system_webview_shell/apk/src/org/chromium/webview_shell/WebViewTracingActivity.java