Make Custom Element registration context creation explicit.

Source/core/loader/DocumentLoader.cpp

Index: Source/core/loader/DocumentLoader.cpp
diff --git a/Source/core/loader/DocumentLoader.cpp b/Source/core/loader/DocumentLoader.cpp
index e53ad70a6e272431e9f5e8053d91e99c8723779e..260a05303bb5078ae1ef963e6a89da0e2ba25e8d 100644
--- a/Source/core/loader/DocumentLoader.cpp
+++ b/Source/core/loader/DocumentLoader.cpp
@@ -796,6 +796,7 @@ PassRefPtr<DocumentWriter> DocumentLoader::createWriterFor(Frame* frame, const D
     // Create a new document before clearing the frame, because it may need to
     // inherit an aliased security context.
     DocumentInit init(url, frame);
+    init.withNewRegistrationContext();
 
     // In some rare cases, we'll re-used a DOMWindow for a new Document. For example,
     // when a script calls window.open("..."), the browser gives JavaScript a window