Add api call to determine whether a string can be externalized.

src/api.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2968 matching lines @@
                              resource,
                              &DisposeExternalString);
   return Utils::ToLocal(result);
 }
 
 
 bool v8::String::MakeExternal(v8::String::ExternalStringResource* resource) {
   if (IsDeadCheck("v8::String::MakeExternal()")) return false;
   if (this->IsExternal()) return false;  // Already an external string.
   ENTER_V8;
-  i::Handle <i::String> obj = Utils::OpenHandle(this);
+  i::Handle<i::String> obj = Utils::OpenHandle(this);
   bool result = obj->MakeExternal(resource);
   if (result && !obj->IsSymbol()) {
     // Operation was successful and the string is not a symbol. In this case
     // we need to make sure that the we call the destructor for the external
     // resource when no strong references to the string remain.
     i::Handle<i::Object> handle = i::GlobalHandles::Create(*obj);
     i::GlobalHandles::MakeWeak(handle.location(),
                                resource,
                                &DisposeExternalString);
   }
@@ skipping 15 matching lines @@
                              &DisposeExternalAsciiString);
   return Utils::ToLocal(result);
 }
 
 
 bool v8::String::MakeExternal(
     v8::String::ExternalAsciiStringResource* resource) {
   if (IsDeadCheck("v8::String::MakeExternal()")) return false;
   if (this->IsExternal()) return false;  // Already an external string.
   ENTER_V8;
-  i::Handle <i::String> obj = Utils::OpenHandle(this);
+  i::Handle<i::String> obj = Utils::OpenHandle(this);
   bool result = obj->MakeExternal(resource);
   if (result && !obj->IsSymbol()) {
     // Operation was successful and the string is not a symbol. In this case
     // we need to make sure that the we call the destructor for the external
     // resource when no strong references to the string remain.
     i::Handle<i::Object> handle = i::GlobalHandles::Create(*obj);
     i::GlobalHandles::MakeWeak(handle.location(),
                                resource,
                                &DisposeExternalAsciiString);
   }
   return result;
 }
 
 
+bool v8::String::CanMakeExternal() {
+  if (IsDeadCheck("v8::String::CanMakeExternal()")) return false;
+  i::Handle<i::String> obj = Utils::OpenHandle(this);
+  int size = obj->Size();  // Byte size of the original string.
+  return (size >= i::ExternalString::kSize) && !obj->IsExternalString();
+}
+
+
 Local<v8::Object> v8::Object::New() {
   EnsureInitialized("v8::Object::New()");
   LOG_API("Object::New");
   ENTER_V8;
   i::Handle<i::JSObject> obj =
       i::Factory::NewJSObject(i::Top::object_function());
   return Utils::ToLocal(obj);
 }
 
 
@@ skipping 588 matching lines @@
       reinterpret_cast<HandleScopeImplementer*>(storage);
   List<void**>* blocks_of_archived_thread = thread_local->Blocks();
   v8::ImplementationUtilities::HandleScopeData* handle_data_of_archived_thread =
       &thread_local->handle_scope_data_;
   Iterate(v, blocks_of_archived_thread, handle_data_of_archived_thread);
 
   return storage + ArchiveSpacePerThread();
 }
 
 } }  // namespace v8::internal