We can switch this on for Debug only. This will help developers
catch bugs more easily, and will only show up for internal
errors and major performance caveats. Currently it's far too easy
to miss these messages - it requires manually modifying debug.h,
looking at a text file and potentially also running Chromium with
an special flag.

BUG=angle:663

Change-Id: I75b3bd05fbc75d21607b9957134db8e8990c77b1
Reviewed-on: https://chromium-review.googlesource.com/239191Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>