Add KVO compliant title property to CWVWebView.

ios/web_view/test/observers/string_observer.mm

Index: ios/web_view/test/observers/string_observer.mm
diff --git a/ios/web_view/test/observers/string_observer.mm b/ios/web_view/test/observers/string_observer.mm
new file mode 100644
index 0000000000000000000000000000000000000000..e1b6e77f66228a1e36cb97a51c7839ffe3c2f1c5
--- /dev/null
+++ b/ios/web_view/test/observers/string_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/string_observer.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+@implementation StringObserver
+
+- (NSString*)lastValue {
+  return self.lastRawValue;
+}
+
+@end