Disable externalization of sliced/cons strings in old pointer space.

This is a temporary workaround for the fact that a good deal of the code that triggers access checks, which in turn externalize strings, is not yet handlified and therefore not GC safe.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/25146008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17023 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/api.cc

@@ -5610,6 +5610,12 @@ bool v8::String::CanMakeExternal() {
   if (!internal::FLAG_clever_optimizations) return false;
   i::Handle<i::String> obj = Utils::OpenHandle(this);
   i::Isolate* isolate = obj->GetIsolate();
+
+  // TODO(yangguo): Externalizing sliced/cons strings allocates.
+  // This rule can be removed when all code that can
+  // trigger an access check is handlified and therefore GC safe.
+  if (isolate->heap()->old_pointer_space()->Contains(*obj)) return false;
+
   if (isolate->string_tracker()->IsFreshUnusedString(obj)) return false;
   int size = obj->Size();  // Byte size of the original string.
   if (size < i::ExternalString::kShortSize) return false;