service_constants: Add SetGlobalOutputChannelRemix property

The new dbus method will be used by Chrome UI to configure
output remix for accessibility use.

BUG=chromium:593218
TEST=None

Change-Id: I7b90a98fecfb3a35f2133e40cf374ffbba96fb9c
Reviewed-on: https://chromium-review.googlesource.com/335011
Commit-Ready: Hsinyu Chao <hychao@chromium.org>
Tested-by: Hsinyu Chao <hychao@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
diff --git a/dbus/service_constants.h b/dbus/service_constants.h
index d1f6ea6..f81a7c5 100644
--- a/dbus/service_constants.h
+++ b/dbus/service_constants.h
@@ -859,6 +859,7 @@
 const char kGetNumberOfActiveStreams[] = "GetNumberOfActiveStreams";
 const char kGetNumberOfActiveInputStreams[] = "GetNumberOfActiveInputStreams";
 const char kGetNumberOfActiveOutputStreams[] = "GetNumberOfActiveOutputStreams";
+const char kSetGlobalOutputChannelRemix[] = "SetGlobalOutputChannelRemix";
 
 // Names of properties returned by GetNodes()
 const char kIsInputProperty[] = "IsInput";