Modify extension request IPC messages to pass a ListValue instead of a string.

chrome/browser/renderer_host/render_view_host_delegate.h

Index: chrome/browser/renderer_host/render_view_host_delegate.h
diff --git a/chrome/browser/renderer_host/render_view_host_delegate.h b/chrome/browser/renderer_host/render_view_host_delegate.h
index 96ed81607fb3531dfa30972544884d4a5def13f0..0f853c39fc52a1dfc23ad4aa53efea8563638a16 100644
--- a/chrome/browser/renderer_host/render_view_host_delegate.h
+++ b/chrome/browser/renderer_host/render_view_host_delegate.h
@@ -19,6 +19,7 @@ class AutofillForm;
 struct ContextMenuParams;
 class FilePath;
 class GURL;
+class Value;
 struct NativeWebKeyboardEvent;
 class NavigationEntry;
 class Profile;
@@ -467,7 +468,7 @@ class RenderViewHostDelegate {
   // A message was sent from HTML-based UI.
   // By default we ignore such messages.
   virtual void ProcessDOMUIMessage(const std::string& message,
-                                   const std::string& content,
+                                   const Value* content,
                                    int request_id,
                                    bool has_callback) {}