Fix background compilation disassembly: allocate string in old space instead of new space.

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index c3d120aea325af253e326b3b8fa4edaf1b809b5c..3b16b3312b2132d24fca362b319be54eab98ed61 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -13798,8 +13798,9 @@ RawString* Code::Name() const {
     Zone* zone = thread->zone();
     const char* name = StubCode::NameOfStub(EntryPoint());
     ASSERT(name != NULL);
-    const String& stub_name = String::Handle(zone, String::New(name));
-    return Symbols::FromConcat(thread, Symbols::StubPrefix(), stub_name);
+    char* stub_name = OS::SCreate(zone,
+        "%s%s", Symbols::StubPrefix().ToCString(), name);
+    return Symbols::New(thread, stub_name, strlen(stub_name));
   } else if (obj.IsClass()) {
     // Allocation stub.
     Thread* thread = Thread::Current();