Invalid chars should not be allowed as first character in custom element name

Source/core/dom/custom/CustomElement.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:
  *
  * 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
@@ skipping 48 matching lines @@
 }
 
 void CustomElement::addEmbedderCustomElementName(const AtomicString& name)
 {
     AtomicString lower = name.lower();
     if (isValidName(lower, EmbedderNames))
         return;
     embedderCustomElementNames().append(lower);
 }
 
+static inline bool isValidNCName(const AtomicString& name)
+{
+    if (kNotFound != name.find(':'))
+        return false;
+
+    if (!name.string().is8Bit()) {
+        const UChar32 c = name.characters16()[0];
+        // These characters comes under CombiningChar in NCName and according to
+        // NCName only BaseChar and Ideodgraphic can come as first chars.
+        // Also these characters come under Letter_Other in UnicodeData, thats
+        // why they pass as valid document name.
+        if (c == 0x0B83 || c == 0x0F88 || c == 0x0F89 || c == 0x0F8A || c == 0x0F8B)
+            return false;
+    }
+
+    return Document::isValidName(name.string());
+}
+
 bool CustomElement::isValidName(const AtomicString& name, NameSet validNames)
 {
     if ((validNames & EmbedderNames) && kNotFound != embedderCustomElementNames().find(name))
         return Document::isValidName(name);
 
     if ((validNames & StandardNames) && kNotFound != name.find('-')) {
         DEFINE_STATIC_LOCAL(Vector<AtomicString>, reservedNames, ());
         if (reservedNames.isEmpty()) {
             // FIXME(crbug.com/426605): We should be able to remove this.
             reservedNames.append(MathMLNames::annotation_xmlTag.localName());
         }
 
         if (kNotFound == reservedNames.find(name))
-            return Document::isValidName(name.string());
+            return isValidNCName(name);
     }
 
     return false;
 }
 
 void CustomElement::define(Element* element, PassRefPtr<CustomElementDefinition> passDefinition)
 {
     RefPtr<CustomElementDefinition> definition(passDefinition);
 
     switch (element->customElementState()) {
@@ skipping 39 matching lines @@
         break;
 
     case Element::WaitingForUpgrade:
     case Element::Upgraded:
         CustomElementObserver::notifyElementWasDestroyed(element);
         break;
     }
 }
 
 } // namespace blink