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

ios/web/public/web_state/web_state_delegate_bridge.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_BRIDGE_H_
+#define IOS_WEB_PUBLIC_WEB_STATE_WEB_STATE_DELEGATE_BRIDGE_H_
+
+#import <Foundation/Foundation.h>
+
+#import "base/ios/weak_nsobject.h"
+#include "ios/web/public/web_state/web_state_delegate.h"
+
+// Objective-C interface for web::WebStateDelegate.
+@protocol CRWWebStateDelegate<NSObject>
+@optional
+
+// Called when the page has made some progress loading. |progress| is a value
+// between 0.0 (nothing loaded) to 1.0 (page fully loaded).
+- (void)webState:(web::WebState*)webState didChangeProgress:(double)progress;
+
+@end
+
+namespace web {
+
+// Adapter to use an id<CRWWebStateDelegate> as a web::WebStateDelegate.
+class WebStateDelegateBridge : public web::WebStateDelegate {
+ public:
+  explicit WebStateDelegateBridge(id<CRWWebStateDelegate> delegate);
+  ~WebStateDelegateBridge() override;
+
+  // web::WebStateDelegate methods.
+  void LoadProgressChanged(WebState* source, double progress) override;
+
+ private:
+  // CRWWebStateDelegate which receives forwarded calls.
+  base::WeakNSProtocol<id<CRWWebStateDelegate>> delegate_;
+  DISALLOW_COPY_AND_ASSIGN(WebStateDelegateBridge);
+};
+
+}  // web
+
+#endif  // IOS_WEB_PUBLIC_WEB_STATE_WEB_STATE_DELEGATE_BRIDGE_H_