Enable fire-and-forget Destroy of HW video decoder, and misc other improvements.

ppapi/thunk/ppb_video_decoder_thunk.cc

Index: ppapi/thunk/ppb_video_decoder_thunk.cc
diff --git a/ppapi/thunk/ppb_video_decoder_thunk.cc b/ppapi/thunk/ppb_video_decoder_thunk.cc
index 434d804fc2521e1419106f871963b9f0c9badd34..996eccaf30bf310209bb0a0bcabc03f7d179e400 100644
--- a/ppapi/thunk/ppb_video_decoder_thunk.cc
+++ b/ppapi/thunk/ppb_video_decoder_thunk.cc
@@ -81,13 +81,11 @@ int32_t Reset(PP_Resource video_decoder,
   return MayForceCallback(callback, result);
 }
 
-int32_t Destroy(PP_Resource video_decoder,
-                PP_CompletionCallback callback) {
+void Destroy(PP_Resource video_decoder) {
   EnterVideoDecoder enter(video_decoder, true);
   if (enter.failed())
-    return MayForceCallback(callback, PP_ERROR_BADRESOURCE);
-  int32_t result = enter.object()->Destroy(callback);
-  return MayForceCallback(callback, result);
+    return;
+  enter.object()->Destroy();
 }
 
 const PPB_VideoDecoder_Dev g_ppb_videodecoder_thunk = {