[iOS] Refactoring web CRWSessionController user agent code.

ios/web/public/test/fakes/test_navigation_manager.mm

Index: ios/web/public/test/fakes/test_navigation_manager.mm
diff --git a/ios/web/public/test/fakes/test_navigation_manager.mm b/ios/web/public/test/fakes/test_navigation_manager.mm
index 38eafcac63a99ee49af5d57b60ac6610730bff3e..0c27847fbd3415d90a2b2f6cf5a1da01a29599ac 100644
--- a/ios/web/public/test/fakes/test_navigation_manager.mm
+++ b/ios/web/public/test/fakes/test_navigation_manager.mm
@@ -139,4 +139,9 @@
   return;
 }
 
+void TestNavigationManager::OverrideDesktopUserAgentForNextPendingItem() {
+  NOTREACHED();
+  return;

[Eugene But (OOO till 7-30), 2017/02/16 02:20:48]

Drop this

[liaoyuke, 2017/02/16 22:04:29]

Done.

+}
+
 }  // namespace web