ANGLE_STATE_VALIDATION_ENABLED is expensive, adding a lot of overhead
to draw calls in debug mode. It's causing some of WebKit's layout tests
to time out. Instead of enabling it for all debug builds, let's only
enable it when ANGLE_ENABLE_DEBUG_TRACE is specified.

Bug: angleproject:3900
Change-Id: I9866d7afbb5666f35c56539820d591953bdf7650
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1994440Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: James Darpinian <jdarpinian@chromium.org>