Mojo C++ Bindings: Extract AssociatedGroupController from MultiplexRouter

mojo/public/cpp/bindings/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 source_set("bindings") {
   sources = [
     "array.h",
     "array_traits.h",
     "array_traits_carray.h",
     "array_traits_standard.h",
     "array_traits_stl.h",
     "associated_binding.h",
     "associated_group.h",
+    "associated_group_controller.h",
     "associated_interface_ptr.h",
     "associated_interface_ptr_info.h",
     "associated_interface_request.h",
     "binding.h",
     "binding_set.h",
     "enum_traits.h",
+    "interface_endpoint_client.h",
+    "interface_endpoint_controller.h",
+    "interface_id.h",
     "interface_ptr.h",
     "interface_ptr_info.h",
     "interface_ptr_set.h",
     "interface_request.h",
     "lib/array_internal.cc",
     "lib/array_internal.h",
     "lib/array_serialization.h",
     "lib/associated_group.cc",
+    "lib/associated_group_controller.cc",
     "lib/associated_interface_ptr_state.h",
     "lib/binding_state.h",
     "lib/bindings_internal.h",
     "lib/buffer.h",
     "lib/connector.cc",
     "lib/connector.h",
     "lib/control_message_handler.cc",
     "lib/control_message_handler.h",
     "lib/control_message_proxy.cc",
     "lib/control_message_proxy.h",
     "lib/filter_chain.cc",
     "lib/filter_chain.h",
     "lib/fixed_buffer.cc",
     "lib/fixed_buffer.h",
     "lib/handle_interface_serialization.h",
     "lib/interface_endpoint_client.cc",
-    "lib/interface_endpoint_client.h",
-    "lib/interface_endpoint_controller.h",
-    "lib/interface_id.h",
     "lib/interface_ptr_state.h",
     "lib/map_data_internal.h",
     "lib/map_serialization.h",
     "lib/message.cc",
     "lib/message_buffer.cc",
     "lib/message_buffer.h",
     "lib/message_builder.cc",
     "lib/message_builder.h",
     "lib/message_filter.cc",
     "lib/message_header_validator.cc",
@@ skipping 96 matching lines @@
     ]
 
     public_deps = [
       ":bindings",
       "//third_party/WebKit/Source/wtf",
     ]
 
     public_configs = [ "//third_party/WebKit/Source:config" ]
   }
 }