When a Virtual Display is plugged in, we create a corresponding surface

whose mutation should be owned by mSyncRoot(Owned by
DisplayManagerService). However, there is an operation of getting the
defaultSize of this Display which is performed without honouring the
mSyncRoot.

Bug: 211153738
Test: Manual
Change-Id: I5bedf0f25dc4635d828b96312f7f799fb9ed321c