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);
+    didAddUserAgentShadowRoot(*shadowRoot);
+    return *shadowRoot;

[eseidel, 2013/11/06 01:11:17]

Who's holding onto this root... Lets hope didAddUserAgentShadowRoot does...
otherwise this looks crashy.

[adamk, 2013/11/06 02:01:39]

addShadowRoot does (ShadowRoot is TreeShared). What interface would you prefer
for this method?

 }
 
 bool Element::childTypeAllowed(NodeType type) const