Revert "Temporarily disable performance.now() in the d8 shell."

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index 25771eed9ba5c28d88d07acace71c1481aa33e9f..1560b09a2b5b77cda7b6592b07be6aa865503f46 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -159,6 +159,7 @@ i::OS::MemoryMappedFile* Shell::counters_file_ = NULL;
 CounterCollection Shell::local_counters_;
 CounterCollection* Shell::counters_ = &local_counters_;
 i::Mutex Shell::context_mutex_;
+const i::TimeTicks Shell::kInitialTicks = i::TimeTicks::HighResolutionNow();
 Persistent<Context> Shell::utility_context_;
 #endif  // V8_SHARED
 
@@ -287,6 +288,15 @@ int PerIsolateData::RealmFind(Handle<Context> context) {
 }
 
 
+#ifndef V8_SHARED
+// performance.now() returns a time stamp as double, measured in milliseconds.
+void Shell::PerformanceNow(const v8::FunctionCallbackInfo<v8::Value>& args) {
+  i::TimeDelta delta = i::TimeTicks::HighResolutionNow() - kInitialTicks;
+  args.GetReturnValue().Set(delta.InMillisecondsF());
+}
+#endif  // V8_SHARED
+
+
 // Realm.current() returns the index of the currently active realm.
 void Shell::RealmCurrent(const v8::FunctionCallbackInfo<v8::Value>& args) {
   Isolate* isolate = args.GetIsolate();
@@ -886,6 +896,14 @@ Handle<ObjectTemplate> Shell::CreateGlobalTemplate(Isolate* isolate) {
                               RealmSharedGet, RealmSharedSet);
   global_template->Set(String::NewFromUtf8(isolate, "Realm"), realm_template);
 
+#ifndef V8_SHARED
+  Handle<ObjectTemplate> performance_template = ObjectTemplate::New(isolate);
+  performance_template->Set(String::NewFromUtf8(isolate, "now"),
+                            FunctionTemplate::New(isolate, PerformanceNow));
+  global_template->Set(String::NewFromUtf8(isolate, "performance"),
+                       performance_template);
+#endif  // V8_SHARED
+
 #if !defined(V8_SHARED) && !defined(_WIN32) && !defined(_WIN64)
   Handle<ObjectTemplate> os_templ = ObjectTemplate::New(isolate);
   AddOSMethods(isolate, os_templ);