Add a corresponding .h file for atom_main.cc.

It's required if we want to include Chromium headers before C headers
and do not break cpplint rules in the meanwhile.

app/atom_main.cc

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "app/atom_main.h"
+
 #include <stdlib.h>
 #include <string.h>
 
@@ -21,8 +23,6 @@
 #include "app/atom_library_main.h"
 #endif  // defined(OS_MACOSX) || defined(OS_LINUX)
 
-#include "content/public/app/content_main.h"
-
 // Declaration of node::Start.
 namespace node {
 int Start(int argc, char *argv[]);

app/atom_main.h

@@ -0,0 +1,5 @@
+// Copyright (c) 2013 GitHub, Inc. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/public/app/content_main.h"

atom.gyp

@@ -4,6 +4,7 @@
     'product_name': 'Atom',
     'app_sources': [
       'app/atom_main.cc',
+      'app/atom_main.h',
     ],
     'bundle_sources': [
       'browser/mac/atom.icns',