Avoid leaking gl::Framebuffers in gl::Context Fix by holding framebuffer via UniqueFramebufferPointer. Removes redundant functions from gl::Surface. Replaces UniqueObjectPointerBase with unique_ptr. The use-case needs default initialization, move assign and operator bool. With these implemented, UniqueObjectPointerBase would have been an imitation of unique_ptr. Patch by David Kilzer <ddkilzer@apple.com> Bug: angleproject:6920 Change-Id: Id0c8fda95f62caa54c89d0a70684e386804db094 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3568382 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Kenneth Russell <kbr@chromium.org>