Add KVO compliant title property to CWVWebView.

ios/web_view/test/observers/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_OBSERVERS_OBSERVER_H_
+#define IOS_WEB_VIEW_TEST_OBSERVERS_OBSERVER_H_
+
+#import <Foundation/Foundation.h>
+
+// A base class to observe a KVO compliant property. To use this Observer, first
+// create an instance of a specialized subclass (depending on the type of
+// |keyPath|) then call |setObservedObject:keyPath:|. You can use this class
+// directly by testing expected values against |lastRawValue|, but prefer to
+// create a subclass similar to BooleanObserver to minimize casting.
+@interface Observer : 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) id lastRawValue;
+
+// 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.
+- (void)setObservedObject:(nonnull NSObject*)object
+                  keyPath:(nonnull NSString*)keyPath;
+
+@end
+
+#endif  // IOS_WEB_VIEW_TEST_OBSERVERS_OBSERVER_H_