Add //mojo/edk/platform/thread_utils.* containing "yield" and "sleep".

mojo/edk/platform/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")
 
 # Declares/defines platform-dependent things. Some things are left
 # unimplemented, and the final binary must include a separate implementation
 # (e.g., //mojo/edk/base_edk, which implements these platform-dependent things
 # using //base).
 mojo_edk_source_set("platform") {
   sources = [
     "io_thread.h",
     "message_loop.h",
     "platform_handle.cc",
     "platform_handle.h",
     "platform_handle_watcher.h",
     "scoped_platform_handle.h",
     "task_runner.h",
     "thread.h",
+    "thread_utils.h",
   ]
 
   mojo_sdk_public_deps = [ "mojo/public/cpp/system" ]
 
   mojo_edk_public_deps = [ "mojo/edk/util" ]
 }
 
 # Functionality to be used by tests (both those merely using :platform as well
 # as those implementing the unimplemented parts of :platform).
 mojo_edk_source_set("test_platform") {
@@ skipping 21 matching lines @@
 # Tests for both :platform and :test_platform. Actually linking these tests into
 # a test binary will require an implementation of :platform and :test_platform
 # (e.g., this is done by //mojo/edk/base_edk:mojo_edk_platform_unittests).
 mojo_edk_source_set("unittests") {
   testonly = true
 
   sources = [
     "aligned_alloc_unittest.cc",
     "io_thread_unittest.cc",
     "test_message_loops_unittest.cc",
+    "thread_utils_unittest.cc",
   ]
 
   deps = [
     ":platform",
     ":test_platform",
     "//testing/gtest",
   ]
 
+  # TODO(vtl): This is a suboptimal dependency. Probably "Stopwatch" should be
+  # moved to :test_platform (which we can do after we add a clock/time function
+  # to :platform).
+  mojo_edk_deps = [ "mojo/edk/system/test" ]
+
   mojo_sdk_deps = [ "mojo/public/cpp/system" ]
 }