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

ios/web/shell/view_controller.mm

Index: ios/web/shell/view_controller.mm
diff --git a/ios/web/shell/view_controller.mm b/ios/web/shell/view_controller.mm
index 5bf37c5942e9dfc12e58a73d464024360385af2c..b1c2a1308abbb0c653c2cd5025f13747577d293e 100644
--- a/ios/web/shell/view_controller.mm
+++ b/ios/web/shell/view_controller.mm
@@ -18,6 +18,7 @@
 #include "ios/web/public/referrer.h"
 #import "ios/web/public/web_controller_factory.h"
 #include "ios/web/public/web_state/web_state.h"
+#import "ios/web/public/web_state/web_state_delegate_bridge.h"
 #import "ios/web/public/web_state/web_state_observer_bridge.h"
 #include "ios/web/shell/shell_browser_state.h"
 #include "ios/web/web_state/ui/crw_web_controller.h"
@@ -30,10 +31,11 @@ NSString* const kWebShellAddressFieldAccessibilityLabel = @"Address field";
 
 using web::NavigationManager;
 
-@interface ViewController ()<CRWWebStateObserver> {
+@interface ViewController ()<CRWWebStateDelegate, CRWWebStateObserver> {
   web::BrowserState* _browserState;
   base::scoped_nsobject<CRWWebController> _webController;
   std::unique_ptr<web::WebStateObserverBridge> _webStateObserver;
+  std::unique_ptr<web::WebStateDelegateBridge> _webStateDelegate;
 
   base::mac::ObjCPropertyReleaser _propertyReleaser_ViewController;
 }
@@ -118,6 +120,8 @@ using web::NavigationManager;
   [_webController setWebUsageEnabled:YES];
 
   _webStateObserver.reset(new web::WebStateObserverBridge(self.webState, self));
+  _webStateDelegate.reset(new web::WebStateDelegateBridge(self));
+  self.webState->SetDelegate(_webStateDelegate.get());
 
   UIView* view = self.webState->GetView();
   [view setFrame:[_containerView bounds]];