Add vda_flag to open chrome

This flag is used in session_manager_setup.sh as well.

BUG=chrome-os-partner:17128
TEST=start factory

Change-Id: I1076f12e3e56c311c33cb51e6b9937f626ea9b37
Reviewed-on: https://gerrit.chromium.org/gerrit/50266
Reviewed-by: Ricky Liang <jcliang@chromium.org>
Commit-Queue: Cheng-Yi Chiang <cychiang@chromium.org>
Tested-by: Cheng-Yi Chiang <cychiang@chromium.org>
diff --git a/py/goofy/test_environment.py b/py/goofy/test_environment.py
index b1e8e96..821765c 100644
--- a/py/goofy/test_environment.py
+++ b/py/goofy/test_environment.py
@@ -116,8 +116,10 @@
     system_info = system.SystemInfo()
     if system_info.architecture == "armv7l":
       accelerated_flag = "--use-gl=egl"
+      vda_flag='--use-exynos-vda'
     else:
       accelerated_flag = "--enable-accelerated-layers"
+      vda_flag=''
 
     # Auto detect the display modes on DUT
     mode_paths = glob.glob('/sys/class/drm/card*/modes')
@@ -145,6 +147,7 @@
       '--enable-audio-mixer',
       '--enable-renderer-side-mixing',
       accelerated_flag,
+      vda_flag,
       ('--default-device-scale-factor=%d' %
        self.goofy.options.ui_scale_factor),
       '--disable-extensions',