Ifdef out the parts of navigation_controller.h that are not supported on iOS.

content/public/browser/navigation_controller.h

Index: content/public/browser/navigation_controller.h
diff --git a/content/public/browser/navigation_controller.h b/content/public/browser/navigation_controller.h
index 27357a6e9083f1d3f543bbd4f0c76d39a4d8c2c6..893887cc37c5e86dc288393563c41995ade2057b 100644
--- a/content/public/browser/navigation_controller.h
+++ b/content/public/browser/navigation_controller.h
@@ -314,6 +314,9 @@ class NavigationController {
 
   // Random --------------------------------------------------------------------
 
+  // Session storage depends on dom_storage that depends on WebKit::WebString,
+  // which cannot be used on iOS.
+#if !defined(OS_IOS)
   // Returns all the SessionStorageNamespace objects that this
   // NavigationController knows about.
   virtual const SessionStorageNamespaceMap&
@@ -322,6 +325,7 @@ class NavigationController {
   // TODO(ajwong): Remove this once prerendering, instant, and session restore
   // are migrated.
   virtual SessionStorageNamespace* GetDefaultSessionStorageNamespace() = 0;
+#endif
 
   // Sets the max restored page ID this NavigationController has seen, if it
   // was restored from a previous session.