Fix ClassLoader issue of WindowContext

The root cause of this issue is that we pass mClassLoader to new created
Resources, but it may be null if we don't set ClassLoader from
container.
This CL fixes this issue by use ContextImpl#getClassLoader instead.

Bug: 203027987
Test: reproducible steps mentioned in bug

Change-Id: Ic88a351b3e9bbcf8382b9aefea63e2be2f190cb6
1 file changed