Adds thunks for getting platform handles

mojo/platform_handle/platform_handle_thunks.cc

+// 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.
+
+#include "mojo/platform_handle/platform_handle_thunks.h"
+
+#include <assert.h>
+
+#if defined(WIN32)
+#define THUNK_EXPORT __declspec(dllexport)
+#else
+#define THUNK_EXPORT __attribute__((visibility("default")))
+#endif
+
+extern "C" {
+
+static MojoPlatformHandleThunks g_thunks = {0};
+
+bool MojoCreatePlatformHandleWrapper(MojoPlatformHandle platform_handle,
+                                     MojoHandle* wrapper) {
+  assert(g_thunks.CreatePlatformHandleWrapper);
+  return g_thunks.CreatePlatformHandleWrapper(platform_handle, wrapper);
+}
+
+bool MojoExtractPlatformHandle(MojoHandle wrapper,
+                               MojoPlatformHandle* platform_handle) {
+  assert(g_thunks.ExtractPlatformHandle);
+  return g_thunks.ExtractPlatformHandle(wrapper, platform_handle);
+}
+
+extern "C" THUNK_EXPORT size_t
+MojoSetPlatformHandleThunks(const MojoPlatformHandleThunks* thunks) {
+  if (thunks->size >= sizeof(g_thunks))
+    g_thunks = *thunks;
+  return sizeof(g_thunks);
+}
+
+}  // extern "C"