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

ios/web/public/test/test_web_state.mm

Index: ios/web/public/test/test_web_state.mm
diff --git a/ios/web/public/test/test_web_state.mm b/ios/web/public/test/test_web_state.mm
index 271c5ecdfce891329223b3d4701825c14e0f3441..6ea998fee93afc93909af1ee7b74aa80fc7d2406 100644
--- a/ios/web/public/test/test_web_state.mm
+++ b/ios/web/public/test/test_web_state.mm
@@ -17,6 +17,12 @@ UIView* TestWebState::GetView() {
   return nullptr;
 }
 
+WebStateDelegate* TestWebState::GetDelegate() {
+  return nil;
+}
+
+void TestWebState::SetDelegate(WebStateDelegate* delegate) {}
+
 WebViewType TestWebState::GetWebViewType() const {
   return web::UI_WEB_VIEW_TYPE;
 }