[serializer] API to re-use global proxy in v8::Context::FromSnapshot.

src/snapshot/partial-serializer.cc

Index: src/snapshot/partial-serializer.cc
diff --git a/src/snapshot/partial-serializer.cc b/src/snapshot/partial-serializer.cc
index 77221badaa2db7ba7b3dbaefc0a3472cde82dfd1..66aafb5368b7c5e907b348363eaf2350e333332c 100644
--- a/src/snapshot/partial-serializer.cc
+++ b/src/snapshot/partial-serializer.cc
@@ -26,9 +26,7 @@ PartialSerializer::~PartialSerializer() {
 void PartialSerializer::Serialize(Object** o, bool include_global_proxy) {
   if ((*o)->IsContext()) {
     Context* context = Context::cast(*o);
-    if (!include_global_proxy) {
-      reference_map()->AddAttachedReference(context->global_proxy());
-    }
+    reference_map()->AddAttachedReference(context->global_proxy());
     // The bootstrap snapshot has a code-stub context. When serializing the
     // partial snapshot, it is chained into the weak context list on the isolate
     // and it's next context pointer may point to the code-stub context.  Clear