Add performance.now() to the d8 shell.

src/d8.h

Index: src/d8.h
diff --git a/src/d8.h b/src/d8.h
index 42013e866d1ef6948ac35ad4e7690d44cf345770..5c7ffaa5bd73ec571a7f603215f0cf3fde2a372f 100644
--- a/src/d8.h
+++ b/src/d8.h
@@ -304,6 +304,8 @@ class Shell : public i::AllStatic {
 #endif  // ENABLE_DEBUGGER_SUPPORT
 #endif  // V8_SHARED
 
+  static void WindowPerformanceNow(
+      const v8::FunctionCallbackInfo<v8::Value>& args);
   static void RealmCurrent(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void RealmOwner(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void RealmGlobal(const v8::FunctionCallbackInfo<v8::Value>& args);
@@ -381,6 +383,7 @@ class Shell : public i::AllStatic {
 
   static const char* kPrompt;
   static ShellOptions options;
+  static const i::TimeTicks kInitialTicks;
 
  private:
   static Persistent<Context> evaluation_context_;