build: add Zuul check pipeline

This pipeline checks the extension with |web-ext lint|.

Change-Id: I3bce686ff33fcbd24c0857da17eccd12458ed2ec
diff --git a/Makefile b/Makefile
index 3f174f1..7b9d980 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-.PHONY: all chromium-stable chromium-beta
+.PHONY: all chromium-stable chromium-beta test-extension
 
 all: chromium-stable chromium-beta
 
@@ -8,5 +8,8 @@
 chromium-beta:
 	bash release.bash -c beta -b chromium
 
+test-extension:
+	bash generateManifest.bash "chromium"
+
 clean:
 	rm -rf out