--verify-predictable mode added for ensuring that GC behaves deterministically.

src/d8.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 
 // Defined when linking against shared lib on Windows.
 #if defined(USING_V8_SHARED) && !defined(V8_SHARED)
 #define V8_SHARED
 #endif
 
@@ skipping 272 matching lines @@
       realms_[index].IsEmpty()) {
     Throw(args.GetIsolate(), "Invalid realm index");
     return -1;
   }
   return index;
 }
 
 
 #ifndef V8_SHARED
 // performance.now() returns a time stamp as double, measured in milliseconds.
+// When FLAG_verify_predictable mode is enabled it returns current value
+// of Heap::allocations_count().
 void Shell::PerformanceNow(const v8::FunctionCallbackInfo<v8::Value>& args) {
-  i::TimeDelta delta = i::TimeTicks::HighResolutionNow() - kInitialTicks;
-  args.GetReturnValue().Set(delta.InMillisecondsF());
+  if (i::FLAG_verify_predictable) {
+    Isolate* v8_isolate = args.GetIsolate();
+    i::Heap* heap = reinterpret_cast<i::Isolate*>(v8_isolate)->heap();
+    args.GetReturnValue().Set(heap->synthetic_time());
+
+  } else {
+    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();
   PerIsolateData* data = PerIsolateData::Get(isolate);
   int index = data->RealmFind(isolate->GetEnteredContext());
   if (index == -1) return;
@@ skipping 1318 matching lines @@
 }
 
 }  // namespace v8
 
 
 #ifndef GOOGLE3
 int main(int argc, char* argv[]) {
   return v8::Shell::Main(argc, argv);
 }
 #endif