[ios] Added web// public API to let embedder observe loading progress.

ios/web/public/web_state/web_state.h

Index: ios/web/public/web_state/web_state.h
diff --git a/ios/web/public/web_state/web_state.h b/ios/web/public/web_state/web_state.h
index 667c8af0f384d3837ab4af90b3472618f333374a..292e778089ba134a536d1e87a6ace0e0b6181548 100644
--- a/ios/web/public/web_state/web_state.h
+++ b/ios/web/public/web_state/web_state.h
@@ -39,6 +39,7 @@ namespace web {
 class BrowserState;
 class NavigationManager;
 class WebInterstitial;
+class WebStateDelegate;
 class WebStateObserver;
 class WebStatePolicyDecider;
 class WebStateWeakPtrFactory;
@@ -84,6 +85,10 @@ class WebState : public base::SupportsUserData {
 
   ~WebState() override {}
 
+  // Gets/Sets the delegate.
+  virtual WebStateDelegate* GetDelegate() = 0;
+  virtual void SetDelegate(WebStateDelegate* delegate) = 0;
+
   // The view containing the contents of the current web page. If the view has
   // been purged due to low memory, this will recreate it. It is up to the
   // caller to size the view.