Move the Kernel string offsets into the VM's heap.

runtime/vm/bootstrap_nocore.cc

 // Copyright (c) 2012, 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/bootstrap.h"
 
 #include "include/dart_api.h"
 
 #if !defined(DART_PRECOMPILED_RUNTIME)
 #include "vm/class_finalizer.h"
@@ skipping 77 matching lines @@
 
   // Load the bootstrap libraries in order (see object_store.h).
   Library& library = Library::Handle(zone);
   String& dart_name = String::Handle(zone);
   for (intptr_t i = 0; i < bootstrap_library_count; ++i) {
     ObjectStore::BootstrapLibraryId id = bootstrap_libraries[i].index;
     library = isolate->object_store()->bootstrap_library(id);
     dart_name = library.url();
     for (intptr_t j = 0; j < program->libraries().length(); ++j) {
       kernel::Library* kernel_library = program->libraries()[j];
-      kernel::String* uri = kernel_library->import_uri();
-      const String& kernel_name = reader.DartSymbol(uri);
+      intptr_t uri_index = kernel_library->import_uri();
+      const String& kernel_name = reader.DartSymbol(uri_index);
       if (kernel_name.Equals(dart_name)) {
         reader.ReadLibrary(kernel_library);
         library.SetLoaded();
         break;
       }
     }
   }
 
   // Finish bootstrapping, including class finalization.
   Finish(thread, /*from_kernel=*/true);
@@ skipping 37 matching lines @@
   return BootstrapFromKernel(thread, program);
 }
 #else
 RawError* Bootstrap::DoBootstrapping(kernel::Program* program) {
   UNREACHABLE();
   return Error::null();
 }
 #endif  // !defined(DART_PRECOMPILED_RUNTIME)
 
 }  // namespace dart