Merge separate definitions of include_dirs for perftests BUG=angleproject:892 Change-Id: Ifd108b3119ea73c05e984ca9138536fb8cf6839c Reviewed-on: https://chromium-review.googlesource.com/273137 Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Corentin Wallez <cwallez@chromium.org>