Implement the file chooser as a new resource "host"

ppapi/proxy/dispatcher.h

Index: ppapi/proxy/dispatcher.h
diff --git a/ppapi/proxy/dispatcher.h b/ppapi/proxy/dispatcher.h
index 797fa08900fdd1a0f8d9c7708ed4e4dde2d1a764..7afaa67f2dd7faf74a5d4e28ed56fe80eba4bccd 100644
--- a/ppapi/proxy/dispatcher.h
+++ b/ppapi/proxy/dispatcher.h
@@ -50,6 +50,8 @@ class PPAPI_PROXY_EXPORT Dispatcher : public ProxyChannel {
   // browser side.
   virtual bool IsPlugin() const = 0;
 
+  void AddFilter(IPC::Channel::Listener* listener);
+
   VarSerializationRules* serialization_rules() const {
     return serialization_rules_.get();
   }
@@ -95,6 +97,9 @@ class PPAPI_PROXY_EXPORT Dispatcher : public ProxyChannel {
     return disallow_trusted_interfaces_;
   }
 
+ protected:
+  std::vector<IPC::Channel::Listener*> filters_;
+
  private:
   friend class HostDispatcherTest;
   friend class PluginDispatcherTest;