Replace base::Callback with base::OnceCallback in base::PendingTask

base/bind.h

Index: base/bind.h
diff --git a/base/bind.h b/base/bind.h
index ce717972e26cde23941d545ef5e3f8832309466e..54209bfab879def0c09224db03109d21fa7b9329 100644
--- a/base/bind.h
+++ b/base/bind.h
@@ -78,6 +78,13 @@ Bind(Functor&& functor, Args&&... args) {
                        std::forward<Args>(args)...);
 }
 
+// Converts a OnceClosure to a RepeatingClosure. It hits CHECK failure to run
+// the resulting RepeatingClosure more than once.
+// TODO(tzik): This will be unneeded after the Closure-to-OnceClosure migration
+// on TaskRunner. Remove it once it gets unneeded.
+BASE_EXPORT RepeatingClosure UnsafeConvertOnceClosureToRepeating(
+    OnceClosure cb);
+
 }  // namespace base
 
 #endif  // BASE_BIND_H_