Add KVO compliant title property to CWVWebView.

ios/web_view/test/boolean_observer.h

-// Copyright 2017 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_VIEW_TEST_BOOLEAN_OBSERVER_H_
-#define IOS_WEB_VIEW_TEST_BOOLEAN_OBSERVER_H_
-
-#import <Foundation/Foundation.h>
-
-// Class to observe a boolean KVO compliant property. To use this object, first
-// create an instance of BooleanObserver and call |setObservedObject:keyPath:|.
-// After an expected change in the value of |keyPath|, ask for |lastValue| and
-// compare to the expected value.
-@interface BooleanObserver : NSObject
-
-// The last value of performing |keyPath| on |object| after being notified of a
-// KVO value change or null if a change has not been observed.
-@property(nonatomic, nullable, readonly) NSNumber* lastValue;
-
-// The |keyPath| of |object| being observed.
-@property(nonatomic, nullable, readonly) NSString* keyPath;
-
-// The current |object| being observed.
-@property(nonatomic, nullable, readonly, weak) NSObject* object;
-
-// Sets the |object| and |keyPath| to observe. Performing |keyPath| on |object|
-// must return a BOOL value and |keyPath| must be KVO compliant.
-// If |object| is null and |self.object| is nonnull, |self.object| will stop
-// being observed. If |object| is nonnull, |keyPath| must be nonnull.
-- (void)setObservedObject:(nullable NSObject*)object
-                  keyPath:(nullable NSString*)keyPath;
-
-@end
-
-#endif  // IOS_WEB_VIEW_TEST_BOOLEAN_OBSERVER_H_