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"
+#include "wtf/text/AtomicStringHash.h"
+#include "wtf/text/StringHash.h"
+
+namespace blink {
+
+TrackDefaultList* TrackDefaultList::create(const HeapVector<Member<TrackDefault>>& trackDefaults, ExceptionState& exceptionState)
+{
+    // Per 11 Dec 2014 Editor's Draft
+    // https://w3c.github.io/media-source/#trackdefaultlist
+    // 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 the same byteStreamTrackID, then throw an
+    //    InvalidAccessError and abort these steps.
+    //    Note: This also applies when byteStreamTrackID contains an empty
+    //    string and ensures that there is only one "byteStreamTrackID
+    //    independent" default for each TrackDefaultType value.
+    using TypeAndID = std::pair<AtomicString, String>;
+    using TypeAndIDToTrackDefaultMap = HeapHashMap<TypeAndID, Member<TrackDefault>>;
+    TypeAndIDToTrackDefaultMap typeAndIDToTrackDefaultMap;
+
+    for (const auto& trackDefault : trackDefaults) {
+        TypeAndID key = TypeAndID(trackDefault->type(), trackDefault->byteStreamTrackID());
+        if (!typeAndIDToTrackDefaultMap.add(key, trackDefault).isNewEntry) {
+            exceptionState.throwDOMException(InvalidAccessError, "Duplicate TrackDefault type (" + key.first + ") and byteStreamTrackID (" + key.second + ")");
+            return nullptr;
+        }
+    }
+
+    // 2. Store a shallow copy of |trackDefaults| in this new object so the values can
+    //    be returned by the accessor methods.
+    // This step is done in constructor initializer.
+    return new TrackDefaultList(trackDefaults);
+}
+
+TrackDefault* TrackDefaultList::item(unsigned index) const
+{
+    // Per 11 Dec 2014 Editor's Draft
+    // https://w3c.github.io/media-source/#trackdefaultlist
+    // 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;
+
+    // 2. Return the |index|'th TrackDefault object in the list.
+    return m_trackDefaults[index].get();
+}
+
+TrackDefaultList::TrackDefaultList(const HeapVector<Member<TrackDefault>>& trackDefaults)
+    : m_trackDefaults(trackDefaults)
+{
+}
+
+void TrackDefaultList::trace(Visitor* visitor)
+{
+    visitor->trace(m_trackDefaults);
+}
+
+} // namespace blink