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

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

Index: Source/core/html/track/vtt/VTTScanner.cpp
diff --git a/Source/core/html/track/vtt/VTTScanner.cpp b/Source/core/html/track/vtt/VTTScanner.cpp
index 4def706a6313b35f4839838e4d1c4141afa9dada..7604794f79d8e6b5ab65c70beaad03f221a7e50e 100644
--- a/Source/core/html/track/vtt/VTTScanner.cpp
+++ b/Source/core/html/track/vtt/VTTScanner.cpp
@@ -168,4 +168,16 @@ bool VTTScanner::scanFloat(float& number)
     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;
+}
+
 }