Fixes shutdown crashes.

runtime/vm/virtual_memory_win.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/globals.h"
 #if defined(TARGET_OS_WINDOWS)
 
 #include "vm/virtual_memory.h"
 
 #include "platform/assert.h"
@@ skipping 15 matching lines @@
   void* address = VirtualAlloc(NULL, size, MEM_RESERVE, PAGE_NOACCESS);
   if (address == NULL) {
     return NULL;
   }
   MemoryRegion region(address, size);
   return new VirtualMemory(region);
 }
 
 
 VirtualMemory::~VirtualMemory() {
-  if (reserved_size_ == 0) {
+  if (embedder_allocated() || (reserved_size_ == 0)) {
     return;
   }
   if (VirtualFree(address(), 0, MEM_RELEASE) == 0) {
     FATAL("VirtualFree failed");
   }
 }
 
 
 bool VirtualMemory::FreeSubSegment(void* address, intptr_t size) {
   // On Windows only the entire segment returned by VirtualAlloc
@@ skipping 41 matching lines @@
   bool result = VirtualProtect(reinterpret_cast<void*>(page_address),
                         end_address - page_address,
                         prot,
                         &old_prot);
   return result;
 }
 
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_WINDOWS)