Mojo C++ bindings: introduce MultiplexRouter and related classes.

mojo/public/cpp/bindings/BUILD.gn

Index: mojo/public/cpp/bindings/BUILD.gn
diff --git a/mojo/public/cpp/bindings/BUILD.gn b/mojo/public/cpp/bindings/BUILD.gn
index 2d4064b52d88636d4281a315519e3bdb5d579fe4..60874fe67caafa74245e00eafec1963913c237ae 100644
--- a/mojo/public/cpp/bindings/BUILD.gn
+++ b/mojo/public/cpp/bindings/BUILD.gn
@@ -30,6 +30,8 @@ source_set("bindings") {
     "lib/filter_chain.h",
     "lib/fixed_buffer.cc",
     "lib/fixed_buffer.h",
+    "lib/interface_endpoint_client.cc",
+    "lib/interface_endpoint_client.h",
     "lib/interface_id.h",
     "lib/interface_ptr_internal.h",
     "lib/map_data_internal.h",
@@ -42,6 +44,8 @@ source_set("bindings") {
     "lib/message_header_validator.cc",
     "lib/message_header_validator.h",
     "lib/message_internal.h",
+    "lib/multiplex_router.cc",
+    "lib/multiplex_router.h",
     "lib/no_interface.cc",
     "lib/pipe_control_message_handler.cc",
     "lib/pipe_control_message_handler.h",
@@ -50,6 +54,8 @@ source_set("bindings") {
     "lib/pipe_control_message_proxy.h",
     "lib/router.cc",
     "lib/router.h",
+    "lib/scoped_interface_endpoint_handle.cc",
+    "lib/scoped_interface_endpoint_handle.h",
     "lib/string_serialization.cc",
     "lib/string_serialization.h",
     "lib/union_accessor.h",