Web MIDI: stop sending messages when the document is going to be closed

third_party/WebKit/Source/modules/webmidi/MIDIAccess.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 180 matching lines @@
   if (portIndex >= m_inputs.size())
     return;
 
   m_inputs[portIndex]->didReceiveMIDIData(portIndex, data, length, timeStamp);
 }
 
 void MIDIAccess::sendMIDIData(unsigned portIndex,
                               const unsigned char* data,
                               size_t length,
                               double timeStampInMilliseconds) {
+  // Do not continue sending when document is going to be closed.
+  Document* document = toDocument(getExecutionContext());
+  DCHECK(document);
+  DocumentLoader* loader = document->loader();
+  if (!loader)
+    return;
+
   if (!data || !length || portIndex >= m_outputs.size())
     return;
+
   // Convert from a time in milliseconds (a DOMHighResTimeStamp) according to
   // the same time coordinate system as performance.now() into a time in seconds
   // which is based on the time coordinate system of
   // monotonicallyIncreasingTime().
   double timeStamp;
 
   if (!timeStampInMilliseconds) {
     // We treat a value of 0 (which is the default value) as special, meaning
     // "now".  We need to translate it exactly to 0 seconds.
     timeStamp = 0;
   } else {
-    Document* document = toDocument(getExecutionContext());
-    DCHECK(document);
-    double documentStartTime =
-        document->loader()->timing().referenceMonotonicTime();
+    double documentStartTime = loader->timing().referenceMonotonicTime();
     timeStamp = documentStartTime + 0.001 * timeStampInMilliseconds;
   }
 
   m_accessor->sendMIDIData(portIndex, data, length, timeStamp);
 }
 
 void MIDIAccess::contextDestroyed() {
   m_accessor.reset();
 }
 
 DEFINE_TRACE(MIDIAccess) {
   visitor->trace(m_inputs);
   visitor->trace(m_outputs);
   EventTargetWithInlineData::trace(visitor);
   SuspendableObject::trace(visitor);
 }
 
 }  // namespace blink