Moves some include definition blocks into constants. Also fixes a
small case error in the capture headers.

Bug: angleproject:2621
Change-Id: I0e5eadcfd8e16969f3502339f58dbf13eb53f43c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2555860Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>