Support is_cfm GN argument

Flag indicates that we can use cfm features in chrome indicating which
files to build and what features to allow.
This USE flag is declared for projects that extend project-cfm-private.

BUG=b:160690338
TEST=Deployed manually

Change-Id: I027f05342560d7dc2da31c875e5f6c481b89afe3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/2285102
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Kyle Williams <kdgwill@chromium.org>
Tested-by: Kyle Williams <kdgwill@chromium.org>
diff --git a/chromeos-base/chromeos-chrome/chromeos-chrome-9999.ebuild b/chromeos-base/chromeos-chrome/chromeos-chrome-9999.ebuild
index ed4cd18..902fc61 100644
--- a/chromeos-base/chromeos-chrome/chromeos-chrome-9999.ebuild
+++ b/chromeos-base/chromeos-chrome/chromeos-chrome-9999.ebuild
@@ -37,6 +37,7 @@
 	+build_tests
 	+chrome_debug
 	+cfi
+	cfm
 	chrome_debug_tests
 	chrome_internal
 	chrome_media
@@ -246,6 +247,8 @@
 		"enable_nacl=$(use_nacl; echotf)"
 		# use_system_minigbm is set below.
 
+		"is_cfm=$(usetf cfm)"
+
 		# Clang features.
 		"is_asan=$(usetf asan)"
 		"is_msan=$(usetf msan)"