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

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..b417e967035b45477285550eea9ab70bdabc2b17 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)
+PassRefPtr<ShadowRoot> ElementShadow::addShadowRoot(Element& shadowHost, ShadowRoot::ShadowRootType type)
 {
     RefPtr<ShadowRoot> shadowRoot = ShadowRoot::create(&shadowHost.document(), type);
 
@@ -149,7 +149,7 @@ ShadowRoot* ElementShadow::addShadowRoot(Element& shadowHost, ShadowRoot::Shadow
     shadowHost.didAddShadowRoot(*shadowRoot);
     InspectorInstrumentation::didPushShadowRoot(&shadowHost, shadowRoot.get());
 
-    return shadowRoot.get();
+    return shadowRoot.release();
 }
 
 void ElementShadow::removeAllShadowRoots()