[Navigation Experiment] Add WKBasedNavigationManagerImpl.

ios/web/navigation/navigation_manager_delegate.h

Index: ios/web/navigation/navigation_manager_delegate.h
diff --git a/ios/web/navigation/navigation_manager_delegate.h b/ios/web/navigation/navigation_manager_delegate.h
index 90c7675c057dbe66f4fb3fee2fe05244a4faba5d..df68122b307d5d4cbba67f34f60c9c9aaf1d9edd 100644
--- a/ios/web/navigation/navigation_manager_delegate.h
+++ b/ios/web/navigation/navigation_manager_delegate.h
@@ -9,6 +9,8 @@
 
 #import "ios/web/public/navigation_manager.h"
 
+@protocol CRWWebViewNavigationProxy;
+
 namespace web {
 
 struct LoadCommittedDetails;
@@ -42,6 +44,10 @@ class NavigationManagerDelegate {
 
   // Returns the WebState associated with this delegate.
   virtual WebState* GetWebState() = 0;
+
+  // Returns a CRWWebViewNavigationProxy protocol that can be used to access
+  // navigation related functions on the main WKWebView.
+  virtual id<CRWWebViewNavigationProxy> GetWebViewNavigationProxy() const = 0;
 };
 
 }  // namespace web