bindings: Add support for the record<K,V> WebIDL type.

third_party/WebKit/Source/core/testing/RecordTest.idl

+// Copyright 2017 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.
+
+typedef record<DOMString, long> RecordTypedef;
+
+interface RecordTest {
+    void setStringLongRecord(RecordTypedef arg);
+    RecordTypedef getStringLongRecord();
+
+    void setNullableStringLongRecord(RecordTypedef? arg);
+    RecordTypedef? getNullableStringLongRecord();
+
+    void setByteStringByteStringRecord(record<ByteString, ByteString> arg);
+
+    void setStringElementRecord(record<DOMString, Element> arg);
+    record<DOMString, Element> getStringElementRecord();
+
+    void setUSVStringUSVStringBooleanRecordRecord(record<USVString, record<USVString, boolean>> arg);
+    record<USVString, record<USVString, boolean>> getUSVStringUSVStringBooleanRecordRecord();
+
+    record<DOMString, sequence<ByteString>> returnStringByteStringSequenceRecord();
+
+    boolean unionReceivedARecord((boolean or record<ByteString, ByteString>) arg);
+
+    // Test the bindings generator code: unions and dictionaries must trace a
+    // record when it's represented as a HeapVector.
+    void setFloatOrStringElementRecord((float or record<DOMString, Element>) arg);
+};