PiP: Hide menu when resize starts.

Attempting to do resize while PIP menu is still visible causes weird
isseus such as jank and flickering, so just hide it. This usually always
happen already when user taps the outside bounds, but if the user starts
from the inside corners it's problematic.

Bug: 164882662
Test: Tap on PIP, see it expands and PIP menu shows up, try to resize -
no more flickering

Change-Id: If32aacc7e8d8f6784ad7fb83be14a8ba93c3491f