This change does two things:

 * only call validation functions once per entry point.
 * move the capture call after the entry point call.

Moving the capure after the call allows us to process the results of
the call. Also we can clean up the validation double call by doing a
bit of entry point refactoring. The code changes shouldn't impact the
resulting code size when capture is disabled.

Bug: angleproject:3611
Change-Id: I9e74ba0a8266903d3e9d1f2eac6acdd2932e5743
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1706561
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>