Do PPB_FileIO Query and Read in the plugin process.

ppapi/shared_impl/tracked_callback.h

Index: ppapi/shared_impl/tracked_callback.h
diff --git a/ppapi/shared_impl/tracked_callback.h b/ppapi/shared_impl/tracked_callback.h
index c4bf5cfd279d3c23fe134835301c94a5001584a3..6f8e9fe37555ee6a331b334390a0eab03e040c8d 100644
--- a/ppapi/shared_impl/tracked_callback.h
+++ b/ppapi/shared_impl/tracked_callback.h
@@ -9,6 +9,7 @@
 #include <set>
 
 #include "base/basictypes.h"
+#include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/synchronization/condition_variable.h"
@@ -84,7 +85,16 @@ class PPAPI_SHARED_EXPORT TrackedCallback
   // callback is targeted to run, it will *not* be run immediately.
   void PostRun(int32_t result);
 
-  void BlockUntilRun();
+  // A task to perform cleanup actions or write output params before calling
+  // back to the plugin. The |result| parameter has the current status, e.g.
+  // whether the operation has been aborted. The return value of the task
+  // becomes the final callback result. The task is always called on the same
+  // thread as the callback to the plugin.
+  typedef base::Callback<int32_t(int32_t /* result */)> CompletionTask;
+
+  // Sets a task that is run just before calling back into the plugin. This
+  // should only be called once.
+  void set_completion_task(const CompletionTask& completion_task);
 
   // Returns the ID of the resource which "owns" the callback, or 0 if the
   // callback is not associated with any resource.
@@ -157,6 +167,9 @@ class PPAPI_SHARED_EXPORT TrackedCallback
   bool aborted_;
   PP_CompletionCallback callback_;
 
+  // Task to run just before calling back into the plugin.
+  CompletionTask completion_task_;
+
   // The MessageLoopShared on which this callback should be run. This will be
   // NULL if we're in-process.
   scoped_refptr<MessageLoopShared> target_loop_;