Add GN support for midl.

third_party/isimpledom/BUILD.gn

Index: third_party/isimpledom/BUILD.gn
diff --git a/third_party/isimpledom/BUILD.gn b/third_party/isimpledom/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..97e80035f3efc6f2958129d91259ae172761f5e4
--- /dev/null
+++ b/third_party/isimpledom/BUILD.gn
@@ -0,0 +1,18 @@
+# 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.
+
+assert(is_win)
+
+import("//build/toolchain/win/midl.gni")
+
+midl("isimpledom") {
+  sources = [
+    "ISimpleDOMDocument.idl",
+    "ISimpleDOMNode.idl",
+    "ISimpleDOMText.idl",
+  ]
+
+  # Note: GYP version sets 'GenerateTypeLibrary': 'false'. It doesn't seem to
+  # be harmful to generate this, however.
+}