[Timeline]: Fixing failure when stop button is pressed before profiler is finished initializing
[Timeline]: Fixing failure when stop button is pressed before profiler is finished initializing

Issue:
- The "Stop" button in the StatusPane is active before the profiler is initialized.
- If a user presses the "Stop" button before initialization is complete, TracingManager.stop will throw an error

Changes:
- The StatusPane's "Stop" button is disabled until profiler initialization is complete

GIFS:
* I added a timeout within the initialization process to better show when the button is disabled.  Initialization is generally a fast process, but if 'Stop' is pressed before completion it will throw an unhandled error
Broken: https://imgur.com/Fjisc8z
Fixed: https://imgur.com/Ad4YegS

Bug: 1072040
Change-Id: Ib770c19a4212a66316d21e2ed242b5401969367c
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2155150
Reviewed-by: Kalon Hinds <0953a07de5dd99912b5643571c8ed9864c017a6d@microsoft.com>
Reviewed-by: Shane Clifford <cefa063138c0abe680fc1b6813cf10cbfcb7387b@microsoft.com>
Commit-Queue: Michael Liao <00d75d81082fdf74688ec453c516b42f7cbf0f40@microsoft.com>

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