LOG_ASSERT needs a message.

This fails to build when asserts are turned on.
diff --git a/media/libmediaplayerservice/TestPlayerStub.cpp b/media/libmediaplayerservice/TestPlayerStub.cpp
index 8627708..aa49429 100644
--- a/media/libmediaplayerservice/TestPlayerStub.cpp
+++ b/media/libmediaplayerservice/TestPlayerStub.cpp
@@ -176,7 +176,7 @@
     mContentUrl = NULL;
 
     if (mPlayer) {
-        LOG_ASSERT(mDeletePlayer != NULL);
+        LOG_ASSERT(mDeletePlayer != NULL, "mDeletePlayer is null");
         (*mDeletePlayer)(mPlayer);
         mPlayer = NULL;
     }