Implement URLSearchParams.

Source/core/dom/DOMURL.h

Index: Source/core/dom/DOMURL.h
diff --git a/Source/core/dom/DOMURL.h b/Source/core/dom/DOMURL.h
index 0f1ddd01fcb1aab7768ea3d07953634f707223db..589dd0142e3d553bcd14bd3d9bddcd7df8b57a75 100644
--- a/Source/core/dom/DOMURL.h
+++ b/Source/core/dom/DOMURL.h
@@ -41,6 +41,7 @@ class ExecutionContext;
 class URLRegistrable;
 
 class DOMURL FINAL : public RefCountedWillBeGarbageCollectedFinalized<DOMURL>, public ScriptWrappable, public DOMURLUtils {
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(DOMURL);
 public:
     static PassRefPtrWillBeRawPtr<DOMURL> create(const String& url, ExceptionState& exceptionState)
     {
@@ -68,7 +69,7 @@ public:
     virtual String input() const OVERRIDE { return m_input; }
     virtual void setInput(const String&) OVERRIDE;
 
-    void trace(Visitor*) { }
+    virtual void trace(Visitor*) OVERRIDE;
 
 private:
     DOMURL(const String& url, const KURL& base, ExceptionState&);