Fix Native Messaging to handle missing caller RenderWidgetHost.

chrome/browser/extensions/api/messaging/native_process_launcher.h

 // Copyright (c) 2012 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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_API_MESSAGING_NATIVE_PROCESS_LAUNCHER_H_
 #define CHROME_BROWSER_EXTENSIONS_API_MESSAGING_NATIVE_PROCESS_LAUNCHER_H_
 
 #include "base/callback_forward.h"
 #include "base/files/file.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 20 matching lines @@
   };
 
   // Callback that's called after the process has been launched. |result| is set
   // to false in case of a failure. Handler must take ownership of the IO
   // handles.
   typedef base::Callback<void(LaunchResult result,
                               base::Process process,
                               base::File read_file,
                               base::File write_file)> LaunchedCallback;
 
+  // Creates default launcher for the current OS. |native_view| refers to the
+  // window that contains calling page. Can be nullptr, e.g. for background
+  // pages.
   static scoped_ptr<NativeProcessLauncher> CreateDefault(
       bool allow_user_level_hosts,
       gfx::NativeView native_view);
 
   NativeProcessLauncher() {}
   virtual ~NativeProcessLauncher() {}
 
   // Finds native messaging host with the specified name and launches it
   // asynchronously. Also checks that the specified |origin| is permitted to
   // access the host. |callback| is called after the process has been started.
@@ skipping 21 matching lines @@
                                   base::File* read_file,
                                   base::File* write_file);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(NativeProcessLauncher);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_MESSAGING_NATIVE_PROCESS_LAUNCHER_H_