Buffer11: Refactor Subject/Observer pattern. Instead of having a direct/static observer distinction, add two messages for 'Contents Changed' and 'Storage Changed'. This makes Buffer11 itself the subject with two different message handling cases in the onSubjectStateChange methods. Bug: angleproject:2389 Change-Id: I645cd4b7cc7ce51cb7f48a01c7fc72939cbe89fe Reviewed-on: https://chromium-review.googlesource.com/957940 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Yuly Novikov <ynovikov@chromium.org>