Fix flakiness of MirroringConfirmationDialogScerenshotTest

The test was flaky because the insets value was racy.
Now it is provided to the view, so screenshot tests will be
deterministic.

Flag: none
Test: MirroringConfirmationDialogTest
Fixes: 308736903
Change-Id: Icd75c319a3eb9bba546f8ff077fdc1ff50ee78ff