Have Element::ensureUserAgentShadowRoot() return a reference

Source/core/dom/shadow/ElementShadow.cpp

Index: Source/core/dom/shadow/ElementShadow.cpp
diff --git a/Source/core/dom/shadow/ElementShadow.cpp b/Source/core/dom/shadow/ElementShadow.cpp
index 158addd3d0da4180463f8863a020789d291d6a10..9ba060d4200f0b72ce11a57f3cf1679944f7775e 100644
--- a/Source/core/dom/shadow/ElementShadow.cpp
+++ b/Source/core/dom/shadow/ElementShadow.cpp
@@ -131,7 +131,7 @@ ElementShadow::~ElementShadow()
     removeAllShadowRoots();
 }
 
-ShadowRoot* ElementShadow::addShadowRoot(Element& shadowHost, ShadowRoot::ShadowRootType type)
+ShadowRoot& ElementShadow::addShadowRoot(Element& shadowHost, ShadowRoot::ShadowRootType type)
 {
     RefPtr<ShadowRoot> shadowRoot = ShadowRoot::create(&shadowHost.document(), type);
 
@@ -149,7 +149,8 @@ ShadowRoot* ElementShadow::addShadowRoot(Element& shadowHost, ShadowRoot::Shadow
     shadowHost.didAddShadowRoot(*shadowRoot);
     InspectorInstrumentation::didPushShadowRoot(&shadowHost, shadowRoot.get());
 
-    return shadowRoot.get();
+    ASSERT(m_shadowRoots.head());

[eseidel, 2013/11/07 23:30:07]

Did you want to ASSERT that m_shadowRoots.head() == shadowRoot.get()?
I guess we could also ASSERT(m_shadowRoots->refCount() > 1) if we really wanted
to.  The ownership in thsi function is just so screwy.

[adamk, 2013/11/08 00:01:51]

The ASSERT you suggest will fail, so it can't be added without making some
actual functional changes to this code.

[Inactive, 2013/11/08 15:09:38]

Well, I really wanted this assertion because I want to make sure I never
dereference a null pointer. However, adding an assertion to make sure
m_shadowRoots.head() == shadowRoot.get() makes a lot of sense as well. I will
add it before landing, thanks.

+    return *m_shadowRoots.head();
 }
 
 void ElementShadow::removeAllShadowRoots()