WebVTT: Support fractional percentage values for position/line/size

Source/core/html/track/vtt/VTTScanner.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 150 matching lines @@
     if (m_is8Bit)
         number = charactersToFloat(integerRun.start(), lengthOfFloat, &validNumber);
     else
         number = charactersToFloat(reinterpret_cast<const UChar*>(integerRun.start()), lengthOfFloat, &validNumber);
 
     if (!validNumber)
         number = std::numeric_limits<float>::max();
     return true;
 }
 
+bool VTTScanner::scanPercentage(float& percentage)
+{
+    Position savedPosition = position();
+    if (!scanFloat(percentage))
+        return false;
+    if (scan('%'))
+        return true;
+    // Restore scanner position.
+    seekTo(savedPosition);
+    return false;
 }
+
+}