The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/671818ff99a8aa6fbf95a3c80d4d456c72892bd3

commit 671818ff99a8aa6fbf95a3c80d4d456c72892bd3
Author: James Cook <jamescook@chromium.org>
Date: Mon Jul 10 19:31:45 2017

chromeos: Make system tray tracing icon work with mash

More go/mustash work. The page chrome://slow allows the user to turn
on performance tracing. This shows an icon in the system tray that
allows the user to navigate back to that page and turn the feature off.

Migrate the code from SystemTrayDelegateChromeOS to SystemTrayClient
and a mojo interface method to make it work with mash.

Add a little test coverage for TrayTracing, which had none.

Bug:  738458 
Test: ash_unittests
Change-Id: I15040b88534d4644c9db288ae1abb2a6b29b30cd
Reviewed-on: https://chromium-review.googlesource.com/558102
Commit-Queue: James Cook <jamescook@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485347}
[modify] https://crrev.com/671818ff99a8aa6fbf95a3c80d4d456c72892bd3/ash/BUILD.gn
[modify] https://crrev.com/671818ff99a8aa6fbf95a3c80d4d456c72892bd3/ash/public/interfaces/system_tray.mojom
[modify] https://crrev.com/671818ff99a8aa6fbf95a3c80d4d456c72892bd3/ash/system/tray/system_tray.cc
[modify] https://crrev.com/671818ff99a8aa6fbf95a3c80d4d456c72892bd3/ash/system/tray/system_tray.h
[modify] https://crrev.com/671818ff99a8aa6fbf95a3c80d4d456c72892bd3/ash/system/tray/system_tray_controller.cc
[modify] https://crrev.com/671818ff99a8aa6fbf95a3c80d4d456c72892bd3/ash/system/tray/system_tray_controller.h
[modify] https://crrev.com/671818ff99a8aa6fbf95a3c80d4d456c72892bd3/ash/system/tray/system_tray_test_api.h
[add] https://crrev.com/671818ff99a8aa6fbf95a3c80d4d456c72892bd3/ash/system/tray_tracing_unittest.cc
[modify] https://crrev.com/671818ff99a8aa6fbf95a3c80d4d456c72892bd3/chrome/browser/chromeos/preferences.cc
[modify] https://crrev.com/671818ff99a8aa6fbf95a3c80d4d456c72892bd3/chrome/browser/ui/ash/system_tray_client.cc
[modify] https://crrev.com/671818ff99a8aa6fbf95a3c80d4d456c72892bd3/chrome/browser/ui/ash/system_tray_client.h
[modify] https://crrev.com/671818ff99a8aa6fbf95a3c80d4d456c72892bd3/chrome/browser/ui/ash/system_tray_delegate_chromeos.cc
[modify] https://crrev.com/671818ff99a8aa6fbf95a3c80d4d456c72892bd3/chrome/browser/ui/ash/system_tray_delegate_chromeos.h