[ios] Added web// public API to let embedder observe loading progress.

ios/web/public/web_state/web_state_delegate.h

+// Copyright 2016 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 IOS_WEB_PUBLIC_WEB_STATE_WEB_STATE_DELEGATE_H_
+#define IOS_WEB_PUBLIC_WEB_STATE_WEB_STATE_DELEGATE_H_
+
+#include <set>
+
+#include "base/callback.h"
+
+namespace net {
+class SSLInfo;
+}
+
+namespace web {
+
+struct SSLStatus;
+class WebState;
+
+// Objects implement this interface to get notified about changes in the
+// WebState and to provide necessary functionality.
+class WebStateDelegate {
+ public:
+  WebStateDelegate();
+
+  // Notifies the delegate that the page has made some progress loading.
+  // |progress| is a value between 0.0 (nothing loaded) to 1.0 (page fully
+  // loaded).
+  virtual void LoadProgressChanged(WebState* source, double progress);
+
+ protected:
+  virtual ~WebStateDelegate();
+
+ private:
+  friend class WebStateImpl;
+
+  // Called when |this| becomes the WebStateDelegate for |source|.
+  void Attach(WebState* source);
+
+  // Called when |this| is no longer the WebStateDelegate for |source|.
+  void Detach(WebState* source);
+
+  // The WebStates for which |this| is currently a delegate.
+  std::set<WebState*> attached_states_;
+};
+
+}  // namespace web
+
+#endif  // IOS_WEB_PUBLIC_WEB_STATE_WEB_STATE_DELEGATE_H_