PPAPI: Make blocking completion callbacks work.

ppapi/proxy/ppb_file_system_proxy.cc

Index: ppapi/proxy/ppb_file_system_proxy.cc
diff --git a/ppapi/proxy/ppb_file_system_proxy.cc b/ppapi/proxy/ppb_file_system_proxy.cc
index 993c468b0ffa200e87204f43ef96bc99a0665944..330b5800a5d73dd91fd08db1fdd83869a6ba0b6d 100644
--- a/ppapi/proxy/ppb_file_system_proxy.cc
+++ b/ppapi/proxy/ppb_file_system_proxy.cc
@@ -47,7 +47,7 @@ class FileSystem : public Resource, public PPB_FileSystem_API {
 
   // PPB_FileSystem_APi implementation.
   virtual int32_t Open(int64_t expected_size,
-                       PP_CompletionCallback callback) OVERRIDE;
+                       ApiCallbackType callback) OVERRIDE;
   virtual PP_FileSystemType GetType() OVERRIDE;
 
   // Called when the host has responded to our open request.
@@ -76,13 +76,13 @@ PPB_FileSystem_API* FileSystem::AsPPB_FileSystem_API() {
 }
 
 int32_t FileSystem::Open(int64_t expected_size,
-                         PP_CompletionCallback callback) {
+                         ApiCallbackType callback) {
   if (TrackedCallback::IsPending(current_open_callback_))
     return PP_ERROR_INPROGRESS;
   if (called_open_)
     return PP_ERROR_FAILED;
 
-  current_open_callback_ = new TrackedCallback(this, callback);
+  current_open_callback_ = callback;
   called_open_ = true;
   PluginDispatcher::GetForResource(this)->Send(
       new PpapiHostMsg_PPBFileSystem_Open(