Utilize PassRefPtr and C++ refs in more places in ShadowRoot code

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index 970023ae3ad900fcba6176b27ef85a343a602223..5e49c3bc3618c09620eee8fcff746afe9430098c 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -1728,13 +1728,13 @@ ShadowRoot* Element::userAgentShadowRoot() const
     return 0;
 }
 
-ShadowRoot* Element::ensureUserAgentShadowRoot()
+ShadowRoot& Element::ensureUserAgentShadowRoot()
 {
     if (ShadowRoot* shadowRoot = userAgentShadowRoot())
-        return shadowRoot;
-    ShadowRoot* shadowRoot = ensureShadow().addShadowRoot(*this, ShadowRoot::UserAgentShadowRoot);
-    didAddUserAgentShadowRoot(shadowRoot);
-    return shadowRoot;
+        return *shadowRoot;
+    RefPtr<ShadowRoot> shadowRoot = ensureShadow().addShadowRoot(*this, ShadowRoot::UserAgentShadowRoot);

[eseidel, 2013/11/06 02:06:09]

If the Shadow is holding onto this as long as it's alive, why would it return a
PassRefPtr from add?  Why not just a raw pointer or a reference?

Why do we hold on to ShadowRoot here if it can't be deallocated by anything we
call?  We definitely don't want to be the last ref to this ShadowRoot or when we
return it it will be dead (since our RefPtr goes out of scope).

+    didAddUserAgentShadowRoot(*shadowRoot);
+    return *shadowRoot;
 }
 
 bool Element::childTypeAllowed(NodeType type) const