Add operator<< for blink::QualifiedName.

It's helpful for logging.
This CL won't affect production.

Change-Id: I9f35d75799ce060ceef34e173967c0881930504d
Reviewed-on: https://chromium-review.googlesource.com/892579Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532793}

third_party/WebKit/Source/core/dom/QualifiedName.cpp

@@ -149,4 +149,11 @@ void QualifiedName::CreateStatic(void* target_address, StringImpl* name) {
       QualifiedName(g_null_atom, AtomicString(name), g_null_atom, true);
 }
 
+std::ostream& operator<<(std::ostream& ostream, const QualifiedName& qname) {
+  ostream << "QualifiedName(local=" << qname.LocalName()
+          << " ns=" << qname.NamespaceURI() << " prefix=" << qname.Prefix()
+          << ")";
+  return ostream;
+}
+
 }  // namespace blink

third_party/WebKit/Source/core/dom/QualifiedName.h

@@ -219,6 +219,8 @@ struct CORE_EXPORT QualifiedNameHash {
   static const bool safe_to_compare_to_empty_or_deleted = false;
 };
 
+CORE_EXPORT std::ostream& operator<<(std::ostream&, const QualifiedName&);
+
 }  // namespace blink
 
 namespace WTF {

third_party/WebKit/Source/core/html/custom/CustomElement.cpp

@@ -119,7 +119,8 @@ HTMLElement* CustomElement::CreateCustomElementSync(
     const QualifiedName& tag_name,
     CustomElementDefinition* definition) {
   DCHECK(ShouldCreateCustomElement(tag_name) ||
-         ShouldCreateCustomizedBuiltinElement(tag_name));
+         ShouldCreateCustomizedBuiltinElement(tag_name))
+      << tag_name;
   HTMLElement* element;
 
   if (definition && definition->Descriptor().IsAutonomous()) {