Protect spy by holding lock

Another thread could access mDisplayContent during setup spy.
That might cause some unexpected error such as:
CannotStubVoidMethodWithReturnValue, WrongTypeOfReturnValue.

Bug: 129331490
Test: atest TaskPositioningControllerTests

Change-Id: I60c7fac1139362957f43254dd0d1740ace28445d
1 file changed