Split ExtensionMessageFilter up into a UI thread part and an IO thread part.

extensions/browser/extension_function.h

Index: extensions/browser/extension_function.h
diff --git a/extensions/browser/extension_function.h b/extensions/browser/extension_function.h
index 0fccce5b50ea12008452f6f079ba180a305977b0..aa2cf84a802b2bf2466d5c9ca9f2c75b8ff70f68 100644
--- a/extensions/browser/extension_function.h
+++ b/extensions/browser/extension_function.h
@@ -41,7 +41,7 @@ class WebContents;
 
 namespace extensions {
 class ExtensionFunctionDispatcher;
-class ExtensionMessageFilter;
+class IOThreadExtensionMessageFilter;
 class QuotaLimitHeuristic;
 }
 
@@ -523,13 +523,14 @@ class IOThreadExtensionFunction : public ExtensionFunction {
   IOThreadExtensionFunction* AsIOThreadExtensionFunction() override;
 
   void set_ipc_sender(
-      base::WeakPtr<extensions::ExtensionMessageFilter> ipc_sender,
+      base::WeakPtr<extensions::IOThreadExtensionMessageFilter> ipc_sender,
       int routing_id) {
     ipc_sender_ = ipc_sender;
     routing_id_ = routing_id;
   }
 
-  base::WeakPtr<extensions::ExtensionMessageFilter> ipc_sender_weak() const {
+  base::WeakPtr<extensions::IOThreadExtensionMessageFilter> ipc_sender_weak()
+      const {
     return ipc_sender_;
   }
 
@@ -554,7 +555,7 @@ class IOThreadExtensionFunction : public ExtensionFunction {
   void SendResponse(bool success) override;
 
  private:
-  base::WeakPtr<extensions::ExtensionMessageFilter> ipc_sender_;
+  base::WeakPtr<extensions::IOThreadExtensionMessageFilter> ipc_sender_;
   int routing_id_;
 
   scoped_refptr<const extensions::InfoMap> extension_info_map_;