Have Node::document() return a reference instead of a pointer

Source/core/html/HTMLMetaElement.cpp

Index: Source/core/html/HTMLMetaElement.cpp
diff --git a/Source/core/html/HTMLMetaElement.cpp b/Source/core/html/HTMLMetaElement.cpp
index a93e2cef7b94cb7683dfc1a2f96fb13dd0959faa..753724ba28755109845866b63b5bae48f26d022e 100644
--- a/Source/core/html/HTMLMetaElement.cpp
+++ b/Source/core/html/HTMLMetaElement.cpp
@@ -77,19 +77,19 @@ void HTMLMetaElement::process()
         return;
 
     if (equalIgnoringCase(name(), "viewport"))
-        document()->processViewport(contentValue, ViewportArguments::ViewportMeta);
+        document().processViewport(contentValue, ViewportArguments::ViewportMeta);
     else if (equalIgnoringCase(name(), "referrer"))
-        document()->processReferrerPolicy(contentValue);
+        document().processReferrerPolicy(contentValue);
     else if (equalIgnoringCase(name(), "handheldfriendly") && equalIgnoringCase(contentValue, "true"))
-        document()->processViewport("width=device-width", ViewportArguments::HandheldFriendlyMeta);
+        document().processViewport("width=device-width", ViewportArguments::HandheldFriendlyMeta);
     else if (equalIgnoringCase(name(), "mobileoptimized"))
-        document()->processViewport("width=device-width, initial-scale=1", ViewportArguments::MobileOptimizedMeta);
+        document().processViewport("width=device-width, initial-scale=1", ViewportArguments::MobileOptimizedMeta);
 
     // Get the document to process the tag, but only if we're actually part of DOM tree (changing a meta tag while
     // it's not in the tree shouldn't have any effect on the document)
     const AtomicString& httpEquivValue = fastGetAttribute(http_equivAttr);
     if (!httpEquivValue.isNull())
-        document()->processHttpEquiv(httpEquivValue, contentValue);
+        document().processHttpEquiv(httpEquivValue, contentValue);
 }
 
 String HTMLMetaElement::content() const