The platform implementation allows the app layer to pass in an
object, on which ANGLE can call virtual methods. Our current
platform will handle trace events, for app profiling, and
histogram records for statistics. The platform approach gives
a much more robust approach than using entry points for every
piece of functionality, and is based on the interop with Blink.

The default platform implementation does a no-op on every call.
The destructor is also private, to ensure we do not call the
destructor of the passed-in class.

BUG=436191

Change-Id: I05641b89a48a9cff81ced059518fceb5aa6c883b
Reviewed-on: https://chromium-review.googlesource.com/248631Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>