Fixes crashes in VM isolate shutdown.

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index d95d307668ba37b42e9980ae11f4ba5dfb406bae..ba35f868122b9002bc03e655c4bdbe3870be8dce 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -378,12 +378,31 @@ static type SpecialCharacter(type value) {
 }
 
 
-void Object::InitOnce(Isolate* isolate) {
+void Object::InitNull(Isolate* isolate) {
   // Should only be run by the vm isolate.
   ASSERT(isolate == Dart::vm_isolate());
 
   // TODO(iposva): NoSafepointScope needs to be added here.
   ASSERT(class_class() == null_);
+
+  Heap* heap = isolate->heap();
+
+  // Allocate and initialize the null instance.
+  // 'null_' must be the first object allocated as it is used in allocation to
+  // clear the object.
+  {
+    uword address = heap->Allocate(Instance::InstanceSize(), Heap::kOld);
+    null_ = reinterpret_cast<RawInstance*>(address + kHeapObjectTag);
+    // The call below is using 'null_' to initialize itself.
+    InitializeObject(address, kNullCid, Instance::InstanceSize());
+  }
+}
+
+
+void Object::InitOnce(Isolate* isolate) {
+  // Should only be run by the vm isolate.
+  ASSERT(isolate == Dart::vm_isolate());
+
   // Initialize the static vtable values.
   {
     Object fake_object;
@@ -418,17 +437,6 @@ void Object::InitOnce(Isolate* isolate) {
   branch_offset_error_ = LanguageError::ReadOnlyHandle();
   vm_isolate_snapshot_object_table_ = Array::ReadOnlyHandle();
 
-
-  // Allocate and initialize the null instance.
-  // 'null_' must be the first object allocated as it is used in allocation to
-  // clear the object.
-  {
-    uword address = heap->Allocate(Instance::InstanceSize(), Heap::kOld);
-    null_ = reinterpret_cast<RawInstance*>(address + kHeapObjectTag);
-    // The call below is using 'null_' to initialize itself.
-    InitializeObject(address, kNullCid, Instance::InstanceSize());
-  }
-
   *null_object_ = Object::null();
   *null_array_ = Array::null();
   *null_string_ = String::null();