Implement seekable() according to the MediaSource specification

Source/modules/mediasource/MediaSource.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 343 matching lines @@
             sourceRanges->add(sourceRanges->start(sourceRanges->length() - 1, ASSERT_NO_EXCEPTION), highestEndTime);
 
         // 5.3 Let new intersection ranges equal the the intersection between the intersection ranges and the source ranges.
         // 5.4 Replace the ranges in intersection ranges with the new intersection ranges.
         intersectionRanges->intersectWith(sourceRanges);
     }
 
     return intersectionRanges.release();
 }
 
+PassRefPtrWillBeRawPtr<TimeRanges> MediaSource::seekable() const
+{
+    // Implements MediaSource algorithm for HTMLMediaElement.seekable.
+    // https://dvcs.w3.org/hg/html-media/raw-file/default/media-source/media-source.html#htmlmediaelement-extensions
+
+    double sourceDuration = duration();
+    // 1. If duration equals NaN then return an empty TimeRanges object.
+    if (std::isnan(sourceDuration))
+        return TimeRanges::create();
+
+    // 2. If duration equals positive Infinity, then return a single range with a start time of 0 and an end time equal to the
+    // highest end time reported by the HTMLMediaElement.buffered attribute.
+    if (sourceDuration == std::numeric_limits<double>::infinity()) {
+        RefPtrWillBeRawPtr<TimeRanges> buffered = m_attachedElement->buffered();
+        if (buffered->length() == 0)

[philipj_slow, 2014/11/11 10:09:02]

The spec doesn't mention this case. If it's impossible, assert so here. If it is
possible, can you file a spec bug to define it?

[Henrik Steen, 2014/11/11 10:42:37]

Filed https://www.w3.org/Bugs/Public/show_bug.cgi?id=27296

+            return TimeRanges::create();
+        return TimeRanges::create(0, buffered->end(buffered->length() - 1, ASSERT_NO_EXCEPTION));
+    }
+
+    // 3. Otherwise, return a single range with a start time of 0 and an end time equal to duration.
+    return TimeRanges::create(0, sourceDuration);
+}
+
 void MediaSource::setDuration(double duration, ExceptionState& exceptionState)
 {
     // 2.1 http://www.w3.org/TR/media-source/#widl-MediaSource-duration
     // 1. If the value being set is negative or NaN then throw an InvalidAccessError
     // exception and abort these steps.
     if (std::isnan(duration)) {
         exceptionState.throwDOMException(InvalidAccessError, ExceptionMessages::notAFiniteNumber(duration, "duration"));
         return;
     }
     if (duration < 0.0) {
@@ skipping 211 matching lines @@
 
     m_asyncEventQueue->enqueueEvent(event.release());
 }
 
 URLRegistry& MediaSource::registry() const
 {
     return MediaSourceRegistry::registry();
 }
 
 } // namespace blink