Make the API name reflect what it does. With recent changes, this get
called from places that are not releasing ImageHelper object, but is try
to reference the current layout. This new name makes more sense than
onImageHelperRelease (at that time when this API was introduced, it was
only called when ImageHelper is being released).

Bug: b/175584609
Change-Id: Ie5f5fcdbd97436724d7eb016374d8b4178e7ba1d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2776261
Commit-Queue: Charlie Lao <cclao@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>