Surface should not be created for WindowContext initially.

Client may create a WindowContext, but without adding a window using
the corresponding WindowToken, initially creating a surface for the
token is very wasteful.
To avoid this, we should only create surfaces when the client is
needed.

Bug: 150813033
Test: atest WindowTokenTests
Test: No system crash when running FocusHandlingTest.
Change-Id: I0def6a436ad9d60948bfb029b3a7b6b44466d068