Add KVO compliant title property to CWVWebView.

ios/web_view/test/observers/boolean_observer.mm

Index: ios/web_view/test/observers/boolean_observer.mm
diff --git a/ios/web_view/test/observers/boolean_observer.mm b/ios/web_view/test/observers/boolean_observer.mm
new file mode 100644
index 0000000000000000000000000000000000000000..601a09dfd030323b872a76889dc9193d33bc1473
--- /dev/null
+++ b/ios/web_view/test/observers/boolean_observer.mm
@@ -0,0 +1,17 @@
+// 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/observers/boolean_observer.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+@implementation BooleanObserver
+
+- (NSNumber*)lastValue {
+  return self.lastRawValue;
+}
+
+@end