run cygwin mount setup in runhooks, and remove some references to it

build/win/setup_cygwin_mount.py

+# 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.
+
+import os
+import sys
+
+def main():
+  if len(sys.argv) != 2 or sys.argv[1] != '--win-only':
+    return 1
+  if 'win' in sys.platform:
+    self_dir = os.path.dirname(sys.argv[0])
+    mount_path = os.path.join(self_dir, "..\\..\\third_party\\cygwin")
+    batch_path = os.path.join(mount_path, "setup_mount.bat")
+    return os.system(os.path.normpath(batch_path) + ">nul")
+  return 0
+
+
+if __name__ == "__main__":
+  sys.exit(main())