Use ChannelMojo for plugin-renderer channels.

content/ppapi_plugin/ppapi_thread.cc

Index: content/ppapi_plugin/ppapi_thread.cc
diff --git a/content/ppapi_plugin/ppapi_thread.cc b/content/ppapi_plugin/ppapi_thread.cc
index ea5e4bc341e1bb6fa2524a3f7a1e4f85b2c32f2c..df2e875bd8db1ee14c2baf6abbfa6aa8bf543e38 100644
--- a/content/ppapi_plugin/ppapi_thread.cc
+++ b/content/ppapi_plugin/ppapi_thread.cc
@@ -39,6 +39,7 @@
 #include "ipc/ipc_platform_file.h"
 #include "ipc/ipc_sync_channel.h"
 #include "ipc/ipc_sync_message_filter.h"
+#include "mojo/public/cpp/system/message_pipe.h"
 #include "ppapi/c/dev/ppp_network_state_dev.h"
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/c/ppp.h"
@@ -492,6 +493,8 @@ bool PpapiThread::SetupChannel(base::ProcessId renderer_pid,
   plugin_handle.name = IPC::Channel::GenerateVerifiedChannelID(
       base::StringPrintf(
           "%d.r%d", base::GetCurrentProcId(), renderer_child_id));
+  mojo::MessagePipe message_pipe;
+  plugin_handle.mojo_handle = message_pipe.handle0.release();
 
   ppapi::proxy::ProxyChannel* dispatcher = NULL;
   bool init_result = false;
@@ -524,14 +527,7 @@ bool PpapiThread::SetupChannel(base::ProcessId renderer_pid,
   }
 
   handle->name = plugin_handle.name;
-#if defined(OS_POSIX)
-  // On POSIX, transfer ownership of the renderer-side (client) FD.
-  // This ensures this process will be notified when it is closed even if a
-  // connection is not established.

[dcheng, 2016/06/27 02:12:48]

How come these checks aren't needed in the Mojo version? What makes it
impossible?

[Anand Mistry (off Chromium), 2016/06/27 02:25:59]

fds are not used when using ChannelMojo (and the returned fd will be -1 and
always fail this check). One day when ChannelMojo rules the world,
TakeRendererFD() and ChannelHandle::socket will both be gone.

[dcheng, 2016/06/27 03:35:02]

OK, so the Mojo handles here are always valid?

[Anand Mistry (off Chromium), 2016/06/27 04:52:07]

Here, yes. But not necessarily in the receive side, so I've added a check to
those.

-  handle->socket = base::FileDescriptor(dispatcher->TakeRendererFD());
-  if (handle->socket.fd == -1)
-    return false;
-#endif
+  handle->mojo_handle = message_pipe.handle1.release();
 
   // From here, the dispatcher will manage its own lifetime according to the
   // lifetime of the attached channel.