web: fix BROWSER=google-chrome on Mac

R=rsc
http://codereview.appspot.com/6750046

bin/web

diff --git a/bin/web b/bin/web
index c4bb51b..8c6fdd4 100755
--- a/bin/web
+++ b/bin/web
@@ -6,6 +6,9 @@
 	none)
 		open "$@"
 		;;
+	*google-chrome*)
+		open -a "Google Chrome" "$@"
+		;;
 	*)
 		open -a "$BROWSER" "$@"
 		;;