mac/linux: rework plugin channel file descriptor creation

chrome/common/plugin_messages_internal.h

Index: chrome/common/plugin_messages_internal.h
diff --git a/chrome/common/plugin_messages_internal.h b/chrome/common/plugin_messages_internal.h
index 500bd938bf9e7fd7816ffb1705290788275e6de2..9eed897e55a81be08e06bfcdd51d65c795691250 100644
--- a/chrome/common/plugin_messages_internal.h
+++ b/chrome/common/plugin_messages_internal.h
@@ -20,19 +20,9 @@ IPC_BEGIN_MESSAGES(PluginProcess)
   // PluginProcessHostMsg_ChannelCreated message.  The renderer's process_id is
   // passed so that the plugin process reuses an existing channel to that
   // process if it exists.
-  // It would be nice to use #ifdefs inside the parameter list to not need to
-  // duplicate this across POSIX/Windows but the Visual Studio compiler doesn't
-  // like that.
-#if defined(OS_WIN)
   IPC_MESSAGE_CONTROL2(PluginProcessMsg_CreateChannel,
                        int /* process_id */,
                        bool /* off_the_record */)
-#elif defined(OS_POSIX)
-  IPC_MESSAGE_CONTROL3(PluginProcessMsg_CreateChannel,
-                       base::FileDescriptor /* socket for new channel */,
-                       int /* process_id */,
-                       bool /* off_the_record */)
-#endif
 
   // Allows a chrome plugin loaded in the browser process to send arbitrary
   // data to an instance of the same plugin loaded in a plugin process.
@@ -57,7 +47,7 @@ IPC_END_MESSAGES(PluginProcess)
 IPC_BEGIN_MESSAGES(PluginProcessHost)
   // Response to a PluginProcessMsg_CreateChannel message.
   IPC_MESSAGE_CONTROL1(PluginProcessHostMsg_ChannelCreated,
-                       std::string /* channel_name */)
+                       IPC::ChannelHandle /* channel_handle */)
 
   IPC_SYNC_MESSAGE_CONTROL0_1(PluginProcessHostMsg_GetPluginFinderUrl,
                               std::string /* plugin finder URL */)