Update testing IDL file to use annotated types

Our parser now supports annotated types and [Clamp] should be associated
with types.

Bug: 714866
Change-Id: I6956e5efcd072a477fb39f0dc6b1c2793bba103a
Reviewed-on: https://chromium-review.googlesource.com/677896Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#503649}

third_party/WebKit/Tools/Scripts/webkitpy/bindings/testdata/test_interface.idl

 [
     CustomToV8
  ] interface Node : EventTarget {
-    [Reflect]const unsigned short ELEMENT_NODE = 1;
-    [Clamp]attribute Node parentNode;
+    [Reflect] const unsigned short ELEMENT_NODE = 1;
+    attribute [Clamp] Node parentNode;
     [Custom] Node appendChild(Node newChild);
 };