Decouple performance() from LocalDOMWindow

Source/modules/webmidi/MIDIOutput.cpp

Index: Source/modules/webmidi/MIDIOutput.cpp
diff --git a/Source/modules/webmidi/MIDIOutput.cpp b/Source/modules/webmidi/MIDIOutput.cpp
index 4a10e4ca676c455dc76d156aa25f277de8df8551..b54d1eef0cfebeefad760b376c18d0f34f0b17e1 100644
--- a/Source/modules/webmidi/MIDIOutput.cpp
+++ b/Source/modules/webmidi/MIDIOutput.cpp
@@ -35,6 +35,7 @@
 #include "core/dom/ExceptionCode.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/frame/LocalDOMWindow.h"
+#include "core/timing/DOMWindowPerformance.h"
 #include "core/timing/Performance.h"
 #include "modules/webmidi/MIDIAccess.h"
 
@@ -45,7 +46,7 @@ namespace {
 double now(ExecutionContext* context)
 {
     LocalDOMWindow* window = context ? context->executingWindow() : 0;
-    Performance* performance = window ? window->performance() : 0;
+    Performance* performance = window ? DOMWindowPerformance::performance(*window) : 0;

[jsbell, 2015/02/12 20:09:06]

Make it nullptr while you're here? (and maybe the line above, too?)

     return performance ? performance->now() : 0.0;
 }