Teach Blink's IDL parser to handle defaulted sequences of strings.

Source/core/testing/InternalDictionary.idl

 // 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.
 
 enum InternalEnum { "foo", "bar", "baz" };
 
 dictionary InternalDictionary {
     long longMember;
     [Clamp] long longMemberWithClamp;
     [EnforceRange] long longMemberWithEnforceRange;
     // We don't want to add a UseCounter feature for testing, so using KeyboardEventKeyLocation.
     [DeprecateAs=KeyboardEventKeyLocation, ImplementedAs=longMember] long deprecateLongMember;
     long longMemberWithDefault = 42;
     long? longOrNullMember;
     long? longOrNullMemberWithDefault = null;
     boolean booleanMember;
     double doubleMember;
     unrestricted double unrestrictedDoubleMember;
     DOMString stringMember;
     DOMString stringMemberWithDefault = "defaultStringValue";
     ByteString byteStringMember;
     USVString usvStringMember;
     sequence<DOMString> stringSequenceMember;
+    sequence<DOMString> stringSequenceMemberWithDefault = [];
     sequence<DOMString>? stringSequenceOrNullMember;
     InternalEnum enumMember;
     InternalEnum enumMemberWithDefault = "foo";
     InternalEnum? enumOrNullMember;
     InternalEnum[] enumArrayMember;
     Element elementMember;
     Element? elementOrNullMember;
     object objectMember;
     object? objectOrNullMemberWithDefault = null;
     (double or DOMString) doubleOrStringMember;
     EventTarget? eventTargetOrNullMember = null;
 };