mshtml: Implement HTMLPerformanceTiming's toString.

dlls/mshtml/omnavigator.c

@@ -1801,8 +1801,10 @@ static HRESULT WINAPI HTMLPerformanceTiming_get_msFirstPaint(IHTMLPerformanceTim
 static HRESULT WINAPI HTMLPerformanceTiming_toString(IHTMLPerformanceTiming *iface, BSTR *string)
 {
     HTMLPerformanceTiming *This = impl_from_IHTMLPerformanceTiming(iface);
-    FIXME("(%p)->(%p)\n", This, string);
-    return E_NOTIMPL;
+
+    TRACE("(%p)->(%p)\n", This, string);
+
+    return dispex_to_string(&This->dispex, string);
 }
 
 static HRESULT WINAPI HTMLPerformanceTiming_toJSON(IHTMLPerformanceTiming *iface, VARIANT *p)

dlls/mshtml/tests/documentmode.js

@@ -218,6 +218,7 @@ sync_test("builtin_toString", function() {
     test("navigator", window.navigator, "Navigator");
     test("performance", window.performance, "Performance");
     test("performanceNavigation", window.performance.navigation, "PerformanceNavigation");
+    test("performanceTiming", window.performance.timing, "PerformanceTiming");
     test("screen", window.screen, "Screen");
     test("sessionStorage", window.sessionStorage, "Storage");
     test("style", document.body.style, "MSStyleCSSProperties");