Introduce few const getters for dom classes

third_party/WebKit/Source/core/dom/Document.cpp

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index 4547e825695e279323896c977797337f33de6009..3e7e308eb5833480e273a71299e1dc4fe8b6bbcf 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -682,6 +682,11 @@ DOMImplementation& Document::implementation()
     return *m_implementation;
 }
 
+DOMImplementation* Document::maybeImplementation() const
+{
+    return m_implementation.get();
+}
+
 bool Document::hasAppCacheManifest() const
 {
     return isHTMLHtmlElement(documentElement()) && documentElement()->hasAttribute(manifestAttr);
@@ -3452,6 +3457,11 @@ StyleSheetList* Document::styleSheets()
     return m_styleSheetList.get();
 }
 
+StyleSheetList* Document::maybeStyleSheets() const
+{
+    return m_styleSheetList;
+}
+
 String Document::preferredStylesheetSet() const
 {
     return m_styleEngine->preferredStylesheetSetName();