Use the return value to signal success for VTTParser helpers

Source/core/html/track/vtt/VTTCue.cpp

 /*
  * Copyright (c) 2013, Opera Software ASA. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 657 matching lines @@
 
     bool isPastNode = true;
     double currentTimestamp = previousTimestamp;
     if (currentTimestamp > movieTime)
         isPastNode = false;
 
     for (Node* child = root->firstChild(); child; child = NodeTraversal::next(*child, root)) {
         if (child->nodeName() == timestampTag) {
             unsigned position = 0;
             String timestamp = child->nodeValue();
-            double currentTimestamp = VTTParser::collectTimeStamp(timestamp, &position);
-            ASSERT(currentTimestamp != -1);
+            double currentTimestamp;
+            bool check = VTTParser::collectTimeStamp(timestamp, &position, currentTimestamp);
+            ASSERT_UNUSED(check, check);
 
             if (currentTimestamp > movieTime)
                 isPastNode = false;
         }
 
         if (child->isVTTElement()) {
             toVTTElement(child)->setIsPastNode(isPastNode);
             // Make an elemenet id match a cue id for style matching purposes.
             if (!id().isEmpty())
                 toElement(child)->setIdAttribute(id());
@@ skipping 408 matching lines @@
     return m_cueBackgroundBox->executionContext();
 }
 
 Document& VTTCue::document() const
 {
     ASSERT(m_cueBackgroundBox);
     return m_cueBackgroundBox->document();
 }
 
 } // namespace WebCore