Chrome Version: 73.0.3641.0
OS: Chrome

Add UMA stats for app dragging and tab dragging, which can include but is not limited to:
For app dragging:
- How many times the user is using app dragging during one user session
- Where does the user put the dragged app, in overview or in split view
- Is splitview active when the drag initiates
- How does the user use app dragging, fling or drag and drop
- The type of apps the user is dragging
- How many times that the user uses the app dragging to close an window
- How many windows in overview when app dragging happens

For tab dragging, it includes all the UMA stats above, and can also include:
- How many tabs are there when the drag initiates
- Does the dragged tab end up in merging into another window or staying as a separate window

.. there might be more UMA stats that I'm missing here.

I'll assign to Min first to add UMA for app dragging, and I'll take it over to add UMA for tab dragging when she is done