Bring in a reduced/simplified version of Chromium's base::WeakPtr to //mojo/edk/util.

mojo/edk/util/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")
 
 # Library of basic things not provided by the C/C++ standard libraries. (These
 # are mostly platform independent. Note: This must not depend on
 # //mojo/edk/platform. TODO(vtl): Maybe the things that aren't really platform
 # independent should be moved to //mojo/edk/platform.)
@@ skipping 14 matching lines @@
     "ref_ptr_internal.h",
     "scoped_file.h",
     "string_number_conversions.cc",
     "string_number_conversions.h",
     "string_printf.cc",
     "string_printf.h",
     "thread_annotations.h",
     "thread_checker.h",
     "waitable_event.cc",
     "waitable_event.h",
+    "weak_ptr.h",
+    "weak_ptr_internal.cc",
+    "weak_ptr_internal.h",
   ]
 
   mojo_sdk_public_deps = [ "mojo/public/cpp/system" ]
 }
 
 # Unit tests for :util. For testing purposes, allow dependence on
 # //mojo/edk/platform; however, using //mojo/edk/platform requires choosing an
 # implementation to get a test binary, which is done below in
 # :mojo_edk_util_unittests.
 mojo_edk_source_set("unittests") {
   testonly = true
 
   sources = [
     "command_line_unittest.cc",
     "cond_var_unittest.cc",
     "mutex_unittest.cc",
     "ref_counted_unittest.cc",
     "string_number_conversions_unittest.cc",
     "string_printf_unittest.cc",
     "thread_annotations_unittest.cc",
     "thread_checker_unittest.cc",
     "waitable_event_unittest.cc",
+    "weak_ptr_unittest.cc",
   ]
 
   deps = [
     ":util",
     "//testing/gtest",
   ]
 
   mojo_sdk_deps = [ "mojo/public/cpp/system" ]
 
   mojo_edk_deps = [
@@ skipping 25 matching lines @@
     ":util",
     "//testing/gtest",
   ]
 
   mojo_edk_deps = [
     "mojo/edk/platform:test_platform",
     "mojo/edk/system/test",
     "mojo/edk/system/test:perf",
   ]
 }