Add KVO compliant title property to CWVWebView.

ios/web_view/internal/cwv_web_view.mm

Index: ios/web_view/internal/cwv_web_view.mm
diff --git a/ios/web_view/internal/cwv_web_view.mm b/ios/web_view/internal/cwv_web_view.mm
index b443c20da523e5297ccc5d965674593f1a3c297e..d228055fae7b63d17c02840bee5d2f45571f6028 100644
--- a/ios/web_view/internal/cwv_web_view.mm
+++ b/ios/web_view/internal/cwv_web_view.mm
@@ -79,6 +79,7 @@ NSString* const kSessionStorageKey = @"sessionStorage";
 @property(nonatomic, readwrite) double estimatedProgress;
 @property(nonatomic, readwrite) BOOL canGoBack;
 @property(nonatomic, readwrite) BOOL canGoForward;
+@property(nonatomic, readwrite, copy) NSString* title;
 
 // Updates the availability of the back/forward navigation properties exposed
 // through |canGoBack| and |canGoForward|.
@@ -95,6 +96,7 @@ static NSString* gUserAgentProduct = nil;
 @synthesize configuration = _configuration;
 @synthesize estimatedProgress = _estimatedProgress;
 @synthesize navigationDelegate = _navigationDelegate;
+@synthesize title = _title;
 @synthesize translationController = _translationController;
 @synthesize UIDelegate = _UIDelegate;
 @synthesize scrollView = _scrollView;
@@ -145,10 +147,6 @@ static NSString* gUserAgentProduct = nil;
   return net::NSURLWithGURL(_webState->GetLastCommittedURL());
 }
 
-- (NSString*)title {
-  return base::SysUTF16ToNSString(_webState->GetTitle());
-}
-
 - (void)goBack {
   if (_webState->GetNavigationManager())
     _webState->GetNavigationManager()->GoBack();
@@ -231,6 +229,10 @@ static NSString* gUserAgentProduct = nil;
   self.estimatedProgress = progress;
 }
 
+- (void)webStateDidChangeTitle:(web::WebState*)webState {
+  self.title = base::SysUTF16ToNSString(_webState->GetTitle());
+}
+
 - (void)renderProcessGoneForWebState:(web::WebState*)webState {
   SEL selector = @selector(webViewWebContentProcessDidTerminate:);
   if ([_navigationDelegate respondsToSelector:selector]) {