Add "webviewupdate" system server service.

Define the service context for "webviewupdate", a new service that will
run in the system server.

Bug: 13005501
Change-Id: I841437c59b362fda88d130be2f2871aef87d9231
diff --git a/service_contexts b/service_contexts
index 4768cf6..7773d26 100644
--- a/service_contexts
+++ b/service_contexts
@@ -112,6 +112,7 @@
 vibrator                                  u:object_r:system_server_service:s0
 voiceinteraction                          u:object_r:system_server_service:s0
 wallpaper                                 u:object_r:system_server_service:s0
+webviewupdate                             u:object_r:system_server_service:s0
 wifip2p                                   u:object_r:system_server_service:s0
 wifiscanner                               u:object_r:system_server_service:s0
 wifi                                      u:object_r:system_server_service:s0