Don't install private script class without a context document

Source/core/html/HTMLMarqueeElement.cpp

Index: Source/core/html/HTMLMarqueeElement.cpp
diff --git a/Source/core/html/HTMLMarqueeElement.cpp b/Source/core/html/HTMLMarqueeElement.cpp
index c17fa69bf2205585b1e89b5c9ca30a54cabbc9da..06d2e178c402b1119619b5cf7ead25b95c1fb5a2 100644
--- a/Source/core/html/HTMLMarqueeElement.cpp
+++ b/Source/core/html/HTMLMarqueeElement.cpp
@@ -34,8 +34,10 @@ namespace blink {
 inline HTMLMarqueeElement::HTMLMarqueeElement(Document& document)
     : HTMLElement(HTMLNames::marqueeTag, document)
 {
-    v8::Handle<v8::Value> classObject = PrivateScriptRunner::installClassIfNeeded(&document, "HTMLMarqueeElement");
-    RELEASE_ASSERT(!classObject.IsEmpty());
+    if (document.contextDocument()) {
+        v8::Handle<v8::Value> classObject = PrivateScriptRunner::installClassIfNeeded(&document, "HTMLMarqueeElement");
+        RELEASE_ASSERT(!classObject.IsEmpty());
+    }
     UseCounter::count(document, UseCounter::HTMLMarqueeElement);
 }