Add infrastructure to keep track of references to prototypes.

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index 218d3b9625880164cc77add838d537432871f628..2645cca9add4191ceac9a7b36d7ec375b758018e 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -116,6 +116,15 @@ Handle<FixedArrayBase> Factory::NewFixedDoubleArrayWithHoles(
 }
 
 
+Handle<WeakFixedArray> Factory::NewWeakFixedArray(int size) {
+  DCHECK(0 <= size);
+  size += WeakFixedArray::kReservedFieldCount;
+  CALL_HEAP_FUNCTION(isolate(), isolate()->heap()->AllocateFixedArrayWithFiller(
+                                    size, NOT_TENURED, Smi::FromInt(0)),
+                     WeakFixedArray);
+}
+
+
 Handle<ConstantPoolArray> Factory::NewConstantPoolArray(
     const ConstantPoolArray::NumberOfEntries& small) {
   DCHECK(small.total_count() > 0);
@@ -1877,7 +1886,7 @@ Handle<JSProxy> Factory::NewJSProxy(Handle<Object> handler,
   // TODO(rossberg): Once we optimize proxies, think about a scheme to share
   // maps. Will probably depend on the identity of the handler object, too.
   Handle<Map> map = NewMap(JS_PROXY_TYPE, JSProxy::kSize);
-  map->set_prototype(*prototype);
+  map->SetPrototype(prototype);
 
   // Allocate the proxy object.
   Handle<JSProxy> result = New<JSProxy>(map, NEW_SPACE);
@@ -1896,7 +1905,7 @@ Handle<JSProxy> Factory::NewJSFunctionProxy(Handle<Object> handler,
   // TODO(rossberg): Once we optimize proxies, think about a scheme to share
   // maps. Will probably depend on the identity of the handler object, too.
   Handle<Map> map = NewMap(JS_FUNCTION_PROXY_TYPE, JSFunctionProxy::kSize);
-  map->set_prototype(*prototype);
+  map->SetPrototype(prototype);
 
   // Allocate the proxy object.
   Handle<JSFunctionProxy> result = New<JSFunctionProxy>(map, NEW_SPACE);
@@ -1921,7 +1930,7 @@ void Factory::ReinitializeJSProxy(Handle<JSProxy> proxy, InstanceType type,
   int size_difference = proxy->map()->instance_size() - map->instance_size();
   DCHECK(size_difference >= 0);
 
-  map->set_prototype(proxy->map()->prototype());
+  map->SetPrototype(handle(proxy->map()->prototype(), proxy->GetIsolate()));
 
   // Allocate the backing storage for the properties.
   int prop_size = map->InitialPropertiesLength();