glmark2 is being included as part of angle_perftests, which is built as
an isolate.

Isolates do not work correctly unless there is a trailing slash for
folders in the data section.

Bug: angleproject:3311
Change-Id: I55e5a655ae15683d5cb070589970ba5d9eba4da0
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1538676
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>