Add KVO compliant title property to CWVWebView.

ios/web_view/test/boolean_observer.mm

-// 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.
-
-#import "ios/web_view/test/boolean_observer.h"
-
-#if !defined(__has_feature) || !__has_feature(objc_arc)
-#error "This file requires ARC support."
-#endif
-
-@implementation BooleanObserver
-
-@synthesize keyPath = _keyPath;
-@synthesize lastValue = _lastValue;
-@synthesize object = _object;
-
-- (void)setObservedObject:(NSObject*)object keyPath:(NSString*)keyPath {
-  [_object removeObserver:self forKeyPath:_keyPath];
-
-  _lastValue = nil;
-  _keyPath = [keyPath copy];
-  _object = object;
-  if (keyPath) {
-    [_object addObserver:self
-              forKeyPath:_keyPath
-                 options:NSKeyValueObservingOptionNew
-                 context:nil];
-  }
-}
-
-- (void)observeValueForKeyPath:(NSString*)keyPath
-                      ofObject:(id)object
-                        change:(NSDictionary<NSKeyValueChangeKey, id>*)change
-                       context:(void*)context {
-  if (![object isEqual:_object] || ![keyPath isEqualToString:_keyPath]) {
-    // Ignore extraneous call from previous |_object| or |_keyPath|.
-    return;
-  }
-  _lastValue = change[NSKeyValueChangeNewKey];
-}
-
-- (void)dealloc {
-  [_object removeObserver:self forKeyPath:_keyPath];
-}
-
-@end