tools/gn: include exec_process.h in the source file.

tools/gn/exec_process_unittest.cc

 // Copyright 2014 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 "tools/gn/exec_process.h"
+
 #include "base/command_line.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/strings/string_util.h"
+#include "build/build_config.h"
 #include "testing/gtest/include/gtest/gtest.h"
-#include "tools/gn/exec_process.h"
 
 #if defined(OS_WIN)
 #include "base/strings/utf_string_conversions.h"
 #endif
 
 namespace internal {
 
 // TODO(cjhopman): Enable these tests when windows ExecProcess handles stderr.
 // 'python' is not runnable on Windows. Adding ["cmd", "/c"] fails because
 // CommandLine does unusual reordering of args.
@@ skipping 99 matching lines @@
       "import sys; sys.stdout.close(); print >>sys.stderr, 'e' * 10000",
       &std_out,
       &std_err,
       &exit_code));
   EXPECT_EQ(0, exit_code);
   EXPECT_EQ(0u, std_out.size());
   EXPECT_EQ(10001u, std_err.size());
 }
 #endif
 }  // namespace internal