PPAPI: Make blocking completion callbacks work.

ppapi/thunk/ppb_host_resolver_private_api.h

Index: ppapi/thunk/ppb_host_resolver_private_api.h
diff --git a/ppapi/thunk/ppb_host_resolver_private_api.h b/ppapi/thunk/ppb_host_resolver_private_api.h
index 367e0c3d01c0e4f47f563c365213391a1f0438d1..446ab205788bb000410fd24086225ff4a6fdd89f 100644
--- a/ppapi/thunk/ppb_host_resolver_private_api.h
+++ b/ppapi/thunk/ppb_host_resolver_private_api.h
@@ -5,10 +5,14 @@
 #ifndef PPAPI_THUNK_PPB_HOST_RESOLVER_PRIVATE_API_H_
 #define PPAPI_THUNK_PPB_HOST_RESOLVER_PRIVATE_API_H_
 
+#include "base/memory/ref_counted.h"
 #include "ppapi/c/private/ppb_host_resolver_private.h"
 #include "ppapi/thunk/ppapi_thunk_export.h"
 
 namespace ppapi {
+
+class TrackedCallback;
+
 namespace thunk {
 
 class PPAPI_THUNK_EXPORT PPB_HostResolver_Private_API {
@@ -18,7 +22,7 @@ class PPAPI_THUNK_EXPORT PPB_HostResolver_Private_API {
   virtual int32_t Resolve(const char* host,
                           uint16_t port,
                           const PP_HostResolver_Private_Hint* hint,
-                          PP_CompletionCallback callback) = 0;
+                          scoped_refptr<TrackedCallback> callback) = 0;
   virtual PP_Var GetCanonicalName() = 0;
   virtual uint32_t GetSize() = 0;
   virtual bool GetNetAddress(uint32_t index,