Fixes crashes in VM isolate shutdown.

runtime/vm/dart.cc

 // Copyright (c) 2013, 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/dart.h"
 
 #include "vm/code_observers.h"
 #include "vm/cpu.h"
 #include "vm/dart_api_state.h"
 #include "vm/dart_entry.h"
@@ skipping 113 matching lines @@
     Dart_IsolateFlags api_flags;
     vm_flags.CopyTo(&api_flags);
     vm_isolate_ = Isolate::Init("vm-isolate", api_flags, is_vm_isolate);
 
     StackZone zone(vm_isolate_);
     HandleScope handle_scope(vm_isolate_);
     Heap::Init(vm_isolate_,
                0,  // New gen size 0; VM isolate should only allocate in old.
                FLAG_old_gen_heap_size * MBInWords,
                FLAG_external_max_size * MBInWords);
+    Object::InitNull(vm_isolate_);
     ObjectStore::Init(vm_isolate_);
     TargetCPUFeatures::InitOnce();
     Object::InitOnce(vm_isolate_);
     ArgumentsDescriptor::InitOnce();
     StubCode::InitOnce();
     // Now that the needed stub has been generated, set the stack limit.
     vm_isolate_->InitializeStackLimit();
     if (vm_isolate_snapshot != NULL) {
       const Snapshot* snapshot = Snapshot::SetupFromBuffer(vm_isolate_snapshot);
       if (snapshot == NULL) {
@@ skipping 164 matching lines @@
   isolate->heap()->EnableGrowthControl();
   isolate->set_init_callback_data(data);
   Api::SetupAcquiredError(isolate);
   if (FLAG_print_class_table) {
     isolate->class_table()->Print();
   }
 
   ServiceIsolate::MaybeInjectVMServiceLibrary(isolate);
 
   ServiceIsolate::SendIsolateStartupMessage();
+  ASSERT(isolate->debugger() != NULL);
   isolate->debugger()->NotifyIsolateCreated();
 
   // Create tag table.
   isolate->set_tag_table(
       GrowableObjectArray::Handle(GrowableObjectArray::New()));
   // Set up default UserTag.
   const UserTag& default_tag = UserTag::Handle(UserTag::DefaultTag());
   isolate->set_current_tag(default_tag);
 
   if (FLAG_keep_code) {
@@ skipping 28 matching lines @@
   return predefined_handles_->handles_.AllocateScopedHandle();
 }
 
 
 bool Dart::IsReadOnlyHandle(uword address) {
   ASSERT(predefined_handles_ != NULL);
   return predefined_handles_->handles_.IsValidScopedHandle(address);
 }
 
 }  // namespace dart