Adds a scavenge GC pass to collect unmodified references

src/api.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.
 
 #include "src/api.h"
 
 #include <string.h>  // For memcpy, strlen.
 #ifdef V8_USE_ADDRESS_SANITIZER
 #include <sanitizer/asan_interface.h>
 #endif  // V8_USE_ADDRESS_SANITIZER
@@ skipping 7511 matching lines @@
 void Isolate::VisitHandlesForPartialDependence(
     PersistentHandleVisitor* visitor) {
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
   i::DisallowHeapAllocation no_allocation;
   VisitorAdapter visitor_adapter(visitor);
   isolate->global_handles()->IterateAllRootsInNewSpaceWithClassIds(
       &visitor_adapter);
 }
 
 
+void Isolate::VisitWeakHandles(PersistentHandleVisitor* visitor) {
+  i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
+  i::DisallowHeapAllocation no_allocation;
+  VisitorAdapter visitor_adapter(visitor);
+  isolate->global_handles()->IterateWeakRootsInNewSpaceWithClassIds(
+      &visitor_adapter);
+}
+
+
 String::Utf8Value::Utf8Value(v8::Local<v8::Value> obj)
     : str_(NULL), length_(0) {
   if (obj.IsEmpty()) return;
   i::Isolate* isolate = i::Isolate::Current();
   Isolate* v8_isolate = reinterpret_cast<Isolate*>(isolate);
   ENTER_V8(isolate);
   i::HandleScope scope(isolate);
   Local<Context> context = v8_isolate->GetCurrentContext();
   TryCatch try_catch(v8_isolate);
   Local<String> str;
@@ skipping 847 matching lines @@
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 }  // namespace internal
 }  // namespace v8