Added usage of ScreenContext in EulaScreen.

components/login/screens/screen_context.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_LOGIN_SCREENS_SCREEN_CONTEXT_H_
 #define COMPONENTS_LOGIN_SCREENS_SCREEN_CONTEXT_H_
 
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
+#include "base/callback.h"
+#include "base/callback_list.h"
+#include "base/containers/hash_tables.h"
 #include "base/containers/hash_tables.h"
 #include "base/logging.h"
 #include "base/memory/linked_ptr.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/strings/string16.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/values.h"
 #include "components/login/base_screen_handler_utils.h"
 #include "components/login/login_export.h"
 
 namespace login {
 
 // ScreenContext is a key-value storage for values that are shared
 // between C++ and JS sides. Objects of this class should be used in
 // the following way:
 //
 // context.SetString("user", "john");
 // context.SetInteger("image-index", 0);
 // context.SetDouble("zoom", 1.25);
 // context.GetChangesAndReset(&dictionary);
 // CallJS("onContextChanged", dictionary);
 //
 // ScreenContext memorizes changed key-value pairs and returns them
 // via GetChangesAndReset() method. After call to this method an
 // internal buffer of changes will be cleared.
 class LOGIN_EXPORT ScreenContext : public base::NonThreadSafe {
  public:
   typedef std::string KeyType;
   typedef base::Value ValueType;
+  typedef base::Callback<void(const KeyType& key, const base::Value& value)>
+      KeyObserver;
+  typedef base::CallbackList<KeyObserver::RunType> KeyObserversList;
+  typedef KeyObserversList::Subscription KeyObserverSubscription;
 
   ScreenContext();
   ~ScreenContext();
 
   bool SetBoolean(const KeyType& key, bool value);
   bool SetInteger(const KeyType& key, int value);
   bool SetDouble(const KeyType& key, double value);
   bool SetString(const KeyType& key, const std::string& value);
   bool SetString(const KeyType& key, const base::string16& value);
   bool SetStringList(const KeyType& key, const StringList& value);
@@ skipping 11 matching lines @@
   base::string16 GetString16(const KeyType& key) const;
   base::string16 GetString16(const KeyType& key,
                              const base::string16& default_value) const;
   StringList GetStringList(const KeyType& key) const;
   StringList GetStringList(const KeyType& key,
                            const StringList& default_value) const;
   String16List GetString16List(const KeyType& key) const;
   String16List GetString16List(const KeyType& key,
                                const String16List& default_value) const;
 
+  scoped_ptr<KeyObserverSubscription> AddKeyObserver(
+      const KeyType& key,
+      const KeyObserver& observer);
+
   // Returns true if context has |key|.
   bool HasKey(const KeyType& key) const;
 
   // Returns true if there was changes since last call to
   // GetChangesAndReset().
   bool HasChanges() const;
 
   // Stores all changes since the last call to the
   // GetChangesAndReset() in |diff|.  All previous contents of |diff|
   // will be thrown away.
@@ skipping 31 matching lines @@
       return default_value;
     return Get<T>(key);
   }
 
   // Contains current state of <key, value> map.
   base::DictionaryValue storage_;
 
   // Contains all pending changes.
   base::DictionaryValue changes_;
 
+  base::hash_map<KeyType, linked_ptr<KeyObserversList>> key_observers_;
+
   DISALLOW_COPY_AND_ASSIGN(ScreenContext);
 };
 
 }  // namespace login
 
 #endif  // COMPONENTS_LOGIN_SCREENS_SCREEN_CONTEXT_H_