Don't update the active cue set in detached Documents

Source/core/html/track/CueTimeline.cpp

 // Copyright 2015 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 "core/html/track/CueTimeline.h"
 
 #include "core/events/Event.h"
 #include "core/html/HTMLMediaElement.h"
 #include "core/html/HTMLTrackElement.h"
@@ skipping 114 matching lines @@
     // 4.8.10.8 Playing the media resource
 
     //  If the current playback position changes while the steps are running,
     //  then the user agent must wait for the steps to complete, and then must
     //  immediately rerun the steps.
     if (ignoreUpdateRequests())
         return;
 
     HTMLMediaElement& mediaElement = this->mediaElement();
 
+    // Don't run the "time marches on" algorithm if the document has been
+    // detached. This primarily guards against dispatch of events w/
+    // HTMLTrackElement targets.
+    if (mediaElement.document().isDetached())

[philipj_slow, 2015/08/12 07:39:33]

Do you think we should make if conditional on !OILPAN? If not this seems like
the kind of code everyone will be afraid to touch because it's no longer
possible to reproduce the original problem.

[fs, 2015/08/12 07:55:45]

I've been pondering whether the (somewhat similar) condition below
(endIgnoringUpdateRequests) should use inDocument() && !isDetached() (maybe even
without the first part if we think that the timeline should be running in
inactive documents). I could make a follow-up to either move this check into
ignoreUpdateRequests, or make all updates go through endIgnoringUpdateRequests
(== always use display-scope).
If we think we'll never hit this w/ Oilpan (dispose replaced by GC) I guess that
would be another possible follow-up (which then may or may not apply below as
well.)

+        return;
+
     // https://html.spec.whatwg.org/#time-marches-on
 
     // 1 - Let current cues be a list of cues, initialized to contain all the
     // cues of all the hidden, showing, or showing by default text tracks of the
     // media element (not the disabled ones) whose start times are less than or
     // equal to the current playback position and whose end times are greater
     // than the current playback position.
     CueList currentCues;
 
     // The user agent must synchronously unset [the text track cue active] flag
@@ skipping 206 matching lines @@
     if (!m_ignoreUpdate && mediaElement().inActiveDocument())
         updateActiveCues(mediaElement().currentTime());
 }
 
 DEFINE_TRACE(CueTimeline)
 {
     visitor->trace(m_mediaElement);
 }
 
 } // namespace blink