Adds GN build files for building in GN based projects.

tools/gn_helpers.py

Index: tools/gn_helpers.py
===================================================================
--- tools/gn_helpers.py	(revision 0)
+++ tools/gn_helpers.py	(revision 0)
@@ -0,0 +1,39 @@
+# 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.
+
+"""Helper functions useful when writing scripts that are run from GN's
+exec_script function."""
+
+class GNException(Exception):
+  pass
+
+
+def ToGNString(value, allow_dicts = True):
+  """Prints the given value to stdout.
+
+  allow_dicts indicates if this function will allow converting dictionaries
+  to GN scopes. This is only possible at the top level, you can't nest a
+  GN scope in a list, so this should be set to False for recursive calls."""
+  if isinstance(value, str):
+    if value.find('\n') >= 0:
+      raise GNException("Trying to print a string with a newline in it.")
+    return '"' + value.replace('"', '\\"') + '"'
+
+  if isinstance(value, list):
+    return '[ %s ]' % ', '.join(ToGNString(v) for v in value)
+
+  if isinstance(value, dict):
+    if not allow_dicts:
+      raise GNException("Attempting to recursively print a dictionary.")
+    result = ""
+    for key in value:
+      if not isinstance(key, str):
+        raise GNException("Dictionary key is not a string.")
+      result += "%s = %s\n" % (key, ToGNString(value[key], False))
+    return result
+
+  if isinstance(value, int):
+    return str(value)
+
+  raise GNException("Unsupported type when printing to GN.")