Introduce a new framework for back-and-forth tracked/protected preferences migration.

base/critical_closure_ios.mm

Index: base/critical_closure_ios.mm
diff --git a/base/critical_closure_ios.mm b/base/critical_closure_ios.mm
index d605cad0a20a5baf076672f07dd4427f43222220..9e537dc37fb2fa365ee910fa78d4e5199ab940b6 100644
--- a/base/critical_closure_ios.mm
+++ b/base/critical_closure_ios.mm
@@ -8,29 +8,27 @@
 
 #include "base/bind.h"
 #include "base/ios/scoped_critical_action.h"
-#include "base/memory/ref_counted.h"
 
 namespace {
 
 // This class wraps a closure so it can continue to run for a period of time
 // when the application goes to the background by using
 // |base::ios::ScopedCriticalAction|.
-class CriticalClosure : public base::RefCountedThreadSafe<CriticalClosure> {
+template <typename R>
+class CriticalClosure {
  public:
-  explicit CriticalClosure(base::Closure* closure) : closure_(closure) {
-  }
+  explicit CriticalClosure(const base::Callback<R(void)>& closure)
+      : closure_(closure) {}
+
+  ~CriticalClosure() {}
 
   void Run() {
-    closure_->Run();
+    closure_.Run();
   }
 
  private:
-  friend class base::RefCountedThreadSafe<CriticalClosure>;
-
-  virtual ~CriticalClosure() {}
-
-  base::ios::ScopedCriticalAction criticial_action_;
-  scoped_ptr<base::Closure> closure_;
+  base::ios::ScopedCriticalAction critical_action_;
+  base::Callback<R(void)> closure_;
 
   DISALLOW_COPY_AND_ASSIGN(CriticalClosure);
 };
@@ -39,11 +37,11 @@ class CriticalClosure : public base::RefCountedThreadSafe<CriticalClosure> {
 
 namespace base {
 
-base::Closure MakeCriticalClosure(const base::Closure& closure) {
+template <typename R>
+Callback<R(void)> MakeCriticalClosure(const Callback<R(void)>& closure) {
   DCHECK([[UIDevice currentDevice] isMultitaskingSupported]);
-  scoped_refptr<CriticalClosure> critical_closure(
-      new CriticalClosure(new base::Closure(closure)));
-  return base::Bind(&CriticalClosure::Run, critical_closure.get());
+  return base::Bind(&CriticalClosure<R>::Run,
+                    Owned(new CriticalClosure<R>(closure)));
 }
 
 }  // namespace base