Added a callback in nuplayer via informational event to signal the start of video rendering

Change-Id: Id7b9b82d4e5467ad8701bfbad4dcc5070f3703cf
diff --git a/media/libmediaplayerservice/nuplayer/NuPlayer.cpp b/media/libmediaplayerservice/nuplayer/NuPlayer.cpp
index 86e122f..8f45491 100644
--- a/media/libmediaplayerservice/nuplayer/NuPlayer.cpp
+++ b/media/libmediaplayerservice/nuplayer/NuPlayer.cpp
@@ -500,6 +500,8 @@
                 CHECK(msg->findInt32("audio", &audio));
 
                 ALOGV("renderer %s flush completed.", audio ? "audio" : "video");
+            } else if (what == Renderer::kWhatVideoRenderingStart) {
+                notifyListener(MEDIA_INFO, MEDIA_INFO_RENDERING_START, 0);
             }
             break;
         }