Add support for dispatch contexts on BindingSet

mojo/public/cpp/bindings/tests/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("tests") {
   testonly = true
 
   sources = [
     "array_common_test.h",
     "array_unittest.cc",
     "associated_interface_unittest.cc",
     "bind_task_runner_unittest.cc",
     "binding_callback_unittest.cc",
+    "binding_set_unittest.cc",
     "binding_unittest.cc",
     "buffer_unittest.cc",
     "connector_unittest.cc",
     "constant_unittest.cc",
     "container_test_util.cc",
     "container_test_util.h",
     "data_view_unittest.cc",
     "equals_unittest.cc",
     "handle_passing_unittest.cc",
     "interface_ptr_unittest.cc",
@@ skipping 113 matching lines @@
 source_set("mojo_public_bindings_test_utils") {
   sources = [
     "validation_test_input_parser.cc",
     "validation_test_input_parser.h",
   ]
 
   deps = [
     "//mojo/public/c/system",
   ]
 }