Introduce mock test system for navigator content utils

Source/modules/navigatorcontentutils/NavigatorContentUtils.h

Index: Source/modules/navigatorcontentutils/NavigatorContentUtils.h
diff --git a/Source/modules/navigatorcontentutils/NavigatorContentUtils.h b/Source/modules/navigatorcontentutils/NavigatorContentUtils.h
index 018e86a58b5fa5375e3e1c0a91923c6cb5b44acb..cc074ea3d14ef3bbf261ad392e0734f24b4486dc 100644
--- a/Source/modules/navigatorcontentutils/NavigatorContentUtils.h
+++ b/Source/modules/navigatorcontentutils/NavigatorContentUtils.h
@@ -47,7 +47,6 @@ public:
     static const char* supplementName();
 
     static void registerProtocolHandler(Navigator&, const String& scheme, const String& url, const String& title, ExceptionState&);
-
     static String isProtocolHandlerRegistered(Navigator&, const String& scheme, const String& url, ExceptionState&);
     static void unregisterProtocolHandler(Navigator&, const String& scheme, const String& url, ExceptionState&);
 
@@ -55,6 +54,8 @@ public:
 
     virtual void trace(Visitor* visitor) OVERRIDE { WillBeHeapSupplement<Page>::trace(visitor); }
 
+    void setClientForTest(PassOwnPtr<NavigatorContentUtilsClient> client) { m_client = client; }
+
 private:
     explicit NavigatorContentUtils(PassOwnPtr<NavigatorContentUtilsClient> client)
         : m_client(client)