I can't understand the metrics.
Can you explains more?
How to get your conclusion?

The intention of the metric is track unintended state machine transition.
When I added the metric, after the state becomes LOADING_EXTENSION, it was expected to move to other state in a short amount of time (waiting for extension loading).
However looking at the high number of the metric (50% of the all #transitions to #LOADING_EXTENSION), it seems it's not running as intended. I guess it's either the metric doesn't report the correct number or the old assumption that LOADING_EXTENSINO is a ephemeral state is no longer true.

I'm afraid I'm not going to work on it as I left the team. Thanks.

Hi Darren,
I talk with oka@ offline. Keigo explain the metrics.
for 
https://uma.googleplex.com/p/chrome/histograms/?endDate=latest&dayCount=7&histograms=VirtualKeyboard.LingeringIntermediateState&fixupData=true&showMax=true&filters=platform%2Ceq%2CC%2Cchannel%2Ceq%2C4%2Cisofficial%2Ceq%2CTrue&implicitFilters=isofficial
This reports 24,325,208.
It means during 7 days, OS loading extension for 24,325,208.

And https://uma.googleplex.com/p/chrome/histograms/?endDate=latest&dayCount=7&histograms=VirtualKeyboard.ControllerStateTransition&fixupData=true&showMax=true&filters=platform%2Ceq%2CC%2Cchannel%2Ceq%2C4%2Cisofficial%2Ceq%2CTrue&implicitFilters=isofficial
This reports INITIAL_to_LOADING_EXTENSION
58,215,555=
If both the metrics are correct, it means VK is in LOADING_EXTENSION state for more than 5 seconds (https://cs.chromium.org/chromium/src/ui/keyboard/keyboard_controller.cc?l=62&rcl=d7a963df511af578c24bf87a66b879883b339547)

It means 24.04% extension loading time exceed 5s. It's unacceptable!

There are three possibilities.
(1) the metrics is not working correctly.
(2) Being in LOADING_EXTENSION state in 5 seconds no longer means "in loading extension from the beging".
(3) Actually the problem is happening.

Darren, please help to figure out it.

I just briefly looked at VirtualKeyboard.InitLatency.FirstLoad [1], which shows that the mean loading time is about 100 - 120 ms. So one of the metrics is wrong. I'll take a look.

[1] https://uma.googleplex.com/p/chrome/histograms/?endDate=latest&dayCount=7&histograms=VirtualKeyboard.InitLatency.FirstLoad&fixupData=true&showMax=true&filters=platform%2Ceq%2CC%2Cchannel%2Ceq%2C4%2Cisofficial%2Ceq%2CTrue&implicitFilters=isofficial