Implement spawnUri from dart:isolate. This function allows us to

runtime/vm/object_store.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object_store.h"
 
 #include "vm/exceptions.h"
 #include "vm/isolate.h"
 #include "vm/object.h"
 #include "vm/raw_object.h"
@@ skipping 52 matching lines @@
     empty_array_(Array::null()),
     symbol_table_(Array::null()),
     canonical_type_arguments_(Array::null()),
     core_library_(Library::null()),
     core_impl_library_(Library::null()),
     isolate_library_(Library::null()),
     mirrors_library_(Library::null()),
     native_wrappers_library_(Library::null()),
     builtin_library_(Library::null()),
     root_library_(Library::null()),
+    import_map_(Array::null()),
     registered_libraries_(Library::null()),
     pending_classes_(GrowableObjectArray::null()),
     sticky_error_(Error::null()),
     empty_context_(Context::null()),
     stack_overflow_(Instance::null()),
     out_of_memory_(Instance::null()),
     keyword_symbols_(Array::null()) {
 }
 
 
@@ skipping 226 matching lines @@
     return kStringInterface;
   } else if (raw_type == list_interface()) {
     return kListInterface;
   } else if (raw_type == byte_array_interface()) {
     return kByteArrayInterface;
   }
   return kInvalidIndex;
 }
 
 }  // namespace dart