Adds methods for Cast support to ios::ChromeBrowserProvider.

ios/public/provider/chrome/browser/chrome_browser_provider.mm

Index: ios/public/provider/chrome/browser/chrome_browser_provider.mm
diff --git a/ios/public/provider/chrome/browser/chrome_browser_provider.mm b/ios/public/provider/chrome/browser/chrome_browser_provider.mm
index df6ca1f753ca9c84d07935416295b852b5213938..691be182ff13715ab0f04ba1300140c0e6f60910 100644
--- a/ios/public/provider/chrome/browser/chrome_browser_provider.mm
+++ b/ios/public/provider/chrome/browser/chrome_browser_provider.mm
@@ -106,6 +106,11 @@ id<AppRatingPrompt> ChromeBrowserProvider::CreateAppRatingPrompt() const {
   return nil;
 }
 
+void ChromeBrowserProvider::InitializeCastService(id main_tab_model) const {}
+
+void ChromeBrowserProvider::AttachTabHelpers(web::WebState* web_state,
+                                             id tab) const {}
+
 bool ChromeBrowserProvider::IsSafeBrowsingEnabled(
     const base::Closure& on_update_callback) {
   return false;