Add serializers for window.performance.

third_party/WebKit/Source/core/timing/Performance.h

Index: third_party/WebKit/Source/core/timing/Performance.h
diff --git a/third_party/WebKit/Source/core/timing/Performance.h b/third_party/WebKit/Source/core/timing/Performance.h
index eef3a9cc6822b4232e547153790d2d46cb9adc7b..69a97265fe22d19ad9c1849ef04bc02f7fb243e8 100644
--- a/third_party/WebKit/Source/core/timing/Performance.h
+++ b/third_party/WebKit/Source/core/timing/Performance.h
@@ -42,6 +42,8 @@
 namespace blink {
 
 class InspectorWebPerfAgent;
+class ScriptState;
+class ScriptValue;
 
 class CORE_EXPORT Performance final : public PerformanceBase,
                                       public DOMWindowProperty {
@@ -63,6 +65,8 @@ class CORE_EXPORT Performance final : public PerformanceBase,
 
   void updateLongTaskInstrumentation() override;
 
+  ScriptValue toJSONForBinding(ScriptState*);
+
   DECLARE_VIRTUAL_TRACE();
 
  private: