Make UNIMPLEMENTED a warning. Having UNIMPLEMENTED be an error was problematic in a few places. Some tests would pass despite hitting the macro. We were relying on this in a bunch of places. Making it a warning is an easier solution than fixing all of the cases. Going forward we can fix the warnings and make warnings produce test failures. This is similar to enabling warnings as errors in C++ code. Bug: angleproject:2552 Change-Id: Iaf0479cd6bd6a9e85aaccbbee13c322166ff7b5a Reviewed-on: https://chromium-review.googlesource.com/1064724 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>