Proliferate gl::Context. This enables a few small things: it will enable making the platform a property of the Display rather than a global. The same goes for the global logging annotator. Also it ensures all back-end implementations have access to the GL / EGL state when available. Also introduces a smart pointer helper class to angleutils for objects that prefer to be destroyed with a context (gl::Context/egl::Display) parameter. We were using std::unique_ptr in a few places that would not work well with these objects. BUG=angleproject:1156 Change-Id: I59e288a3d6f766ff8a0f4b48ff3a1fbf7489daba Reviewed-on: https://chromium-review.googlesource.com/529706 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>