Re-land: [mojo-edk] Serialise windows handles into an "extra header" section.

mojo/edk/system/channel_win.cc

 // Copyright 2016 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/edk/system/channel.h"
 
 #include <stdint.h>
 #include <windows.h>
 
 #include <algorithm>
@@ skipping 103 matching lines @@
     if (write_error) {
       // Do not synchronously invoke OnError(). Write() may have been called by
       // the delegate and we don't want to re-enter it.
       io_task_runner_->PostTask(FROM_HERE,
                                 base::Bind(&ChannelWin::OnError, this));
     }
   }
 
   ScopedPlatformHandleVectorPtr GetReadPlatformHandles(
       size_t num_handles,
-      void** payload,
-      size_t* payload_size) override {
+      const void* extra_header,
+      size_t extra_header_size) override {
     size_t handles_size = sizeof(PlatformHandle) * num_handles;
-    if (handles_size > *payload_size)
+    if (handles_size > extra_header_size)
       return nullptr;
 
-    *payload_size -= handles_size;
     ScopedPlatformHandleVectorPtr handles(
         new PlatformHandleVector(num_handles));
-    memcpy(handles->data(),
-           static_cast<const char*>(*payload) + *payload_size, handles_size);
+    memcpy(handles->data(), extra_header, handles_size);
     return handles;
   }
 
  private:
   // May run on any thread.
   ~ChannelWin() override {
     // This is intentionally not 0. If another object is constructed on top of
     // this memory, it is likely to initialise values to 0. Using a non-zero
     // value lets us detect the difference between just destroying, and
     // re-allocating the memory.
@@ skipping 174 matching lines @@
 // static
 scoped_refptr<Channel> Channel::Create(
     Delegate* delegate,
     ScopedPlatformHandle platform_handle,
     scoped_refptr<base::TaskRunner> io_task_runner) {
   return new ChannelWin(delegate, std::move(platform_handle), io_task_runner);
 }
 
 }  // namespace edk
 }  // namespace mojo