PPAPI: Make blocking completion callbacks work.

ppapi/thunk/ppb_video_capture_thunk.cc

Index: ppapi/thunk/ppb_video_capture_thunk.cc
diff --git a/ppapi/thunk/ppb_video_capture_thunk.cc b/ppapi/thunk/ppb_video_capture_thunk.cc
index 66ea4bcdb57e2986e8d4e9af0413383a07419dcf..a236986f18a3b8fa32a1d38d524c63f2858acc49 100644
--- a/ppapi/thunk/ppb_video_capture_thunk.cc
+++ b/ppapi/thunk/ppb_video_capture_thunk.cc
@@ -36,7 +36,8 @@ int32_t EnumerateDevices(PP_Resource video_capture,
   if (enter.failed())
     return enter.retval();
 
-  return enter.SetResult(enter.object()->EnumerateDevices(devices, callback));
+  return enter.SetResult(enter.object()->EnumerateDevices(devices,
+                                                          enter.callback()));
 }
 
 int32_t Open(PP_Resource video_capture,
@@ -59,7 +60,7 @@ int32_t Open(PP_Resource video_capture,
   }
 
   return enter.SetResult(enter.object()->Open(
-      device_id, *requested_info, buffer_count, callback));
+      device_id, *requested_info, buffer_count, enter.callback()));
 }
 
 int32_t StartCapture(PP_Resource video_capture) {