EDK: Add a mojo::platform::MessageLoop abstraction.

mojo/edk/base_edk/BUILD.gn

 # Copyright 2015 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.
 
 import("../mojo_edk.gni")
 
 mojo_edk_source_set("base_edk") {
   sources = [
+    "platform_message_loop_impl.cc",
+    "platform_message_loop_impl.h",
     "platform_task_runner_impl.cc",
     "platform_task_runner_impl.h",
   ]
 
   deps = [
     "//base",
   ]
 
   mojo_edk_public_deps = [ "mojo/edk/platform" ]
 }
+
+mojo_edk_source_set("test_base_edk") {
+  testonly = true
+
+  sources = [
+    "test_message_loop.cc",
+  ]
+
+  deps = [
+    ":base_edk",
+  ]
+
+  mojo_edk_public_deps = [
+    "mojo/edk/platform",
+    "mojo/edk/platform:test_platform",
+  ]
+}
+
+mojo_edk_unittests("mojo_edk_base_edk_unittests") {
+  sources = [
+    "platform_message_loop_impl_unittest.cc",
+  ]
+
+  deps = [
+    ":base_edk",
+    ":test_base_edk",
+    "//base",
+    "//testing/gtest",
+  ]
+
+  mojo_edk_deps = [
+    "mojo/edk/platform",
+    "mojo/edk/util",
+  ]
+}