This error showed because DecorContext uses application context
to get WindowManager. This CL changes to use PhoneWindow to obtain
WindowManager instance. Also refactor ctr to obtain context from
PhoneWindow.
Bug: 152806048
Test: manual - enable strict mode and check the error log not shown.
Test: atest DecorContextTest
Test: atest MemoryTests#testActivityRecreation
Change-Id: I1d416b9cdb015c9bc3553571041f3b14bb9da5da