MSE: Implement TrackDefaultList object

Source/modules/mediasource/TrackDefaultList.cpp

+// 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.
+
+#include "config.h"
+
+#include "modules/mediasource/TrackDefaultList.h"
+
+#include "bindings/core/v8/ExceptionState.h"
+#include "core/dom/ExceptionCode.h"
+
+namespace blink {
+
+TrackDefault* TrackDefaultList::item(unsigned long index) const
+{
+    // Per 06 Oct 2014 Editor's Draft
+    // https://dvcs.w3.org/hg/html-media/raw-file/tip/media-source/media-source.html#widl-TrackDefaultList-TrackDefault-getter-unsigned-long-index
+    // When this method is invoked, the user agent must run the following steps:
+    // 1. If index is greater than or equal to the length attribute then return
+    //    undefined and abort these steps.
+    if (index >= m_trackDefaults.size())
+        return 0;

[philipj_slow, 2014/11/14 12:12:27]

Without custom bindings, I'm guessing this will return null, not undefined.
There's a spec problem here, though. The return type is TrackDefault, which
allows neither undefined nor null. A nullable TrackDefault? would allow null.

[wolenetz, 2014/12/03 01:09:56]

See discussion outside this comment, in this CL.

+
+    // 2. Return the |index|'th TrackDefault object in the list.
+    return m_trackDefaults[index].get();
+}
+
+TrackDefaultList::TrackDefaultList(const Vector<TrackDefault>& trackDefaults, ExceptionState& exceptionState)
+{
+    // Per 06 Oct 2014 Editor's Draft
+    // https://dvcs.w3.org/hg/html-media/raw-file/tip/media-source/media-source.html#widl-ctor-TrackDefaultList--sequence-TrackDefault--trackDefaults
+    // When this method is invoked, the user agent must run the following steps:
+    // 1. If |trackDefaults| contains two or more TrackDefault objects with the
+    //    same type and have byteStreamTrackID equal to an empty string, then
+    //    throw an INVALID_ACCESS_ERR and abort these steps.
+    //    Note: This ensures that there is only one "byteStreamTrackID
+    //    independent" default for each TrackDefaultType value.
+    // FIXME: What if two same non-empty track ID entries have the same type?
+    // This could lead to ambiguity in the default track {language, label,
+    // kinds} algorithms. This seems to be a spec bug. Pinged acolwell@ 04 Nov
+    // 2014.
+    // BIG TODO: implement
+
+    // 2. Store a copy of |trackDefaults| in this new object so the values can
+    //    be returned by the accessor methods.
+    // BIG TODO: test this, and test that a subsequent change of the initial constructor
+    // sequence parameter does NOT change the contents of this list.
+    // BIG TODO: implement
+}
+
+} // namespace blink