Rename ScreeManagerOzone to ScreenManagerOzoneInternal

CL renames ScreeManagerOzone to ScreenManagerOzoneInternal,
and ScreeManagerStub to ScreenManagerStubInternal to reflect
their current 'internal window mode' purposes.

Eventually, we will have a ScreenManagerOzoneExternal class,
which should support 'external window mode' with Mus.

BUG=666958

Review-Url: https://codereview.chromium.org/2685003002
Cr-Commit-Position: refs/heads/master@{#449168}
6 files changed