Fail with fatal error instead of segmentation fault if virtual memory allocation fails.

runtime/vm/virtual_memory.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/virtual_memory.h"
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 
 namespace dart {
 
 VirtualMemory* VirtualMemory::ReserveAligned(intptr_t size,
                                              intptr_t alignment) {
   ASSERT((size & (PageSize() - 1)) == 0);
   ASSERT(Utils::IsPowerOfTwo(alignment));
   ASSERT(alignment >= PageSize());
   VirtualMemory* result = VirtualMemory::Reserve(size + alignment);
+  if (result == NULL) {
+    FATAL("Out of memory.\n");
+  }
   uword start = result->start();
   uword real_start = (start + alignment - 1) & ~(alignment - 1);
   result->Truncate(real_start, size);
   return result;
 }
 
 
 void VirtualMemory::Truncate(uword new_start, intptr_t new_size) {
   ASSERT(new_start >= start());
   ASSERT((new_size & (PageSize() - 1)) == 0);
   if (new_start > start()) {
     uword split = new_start - start();
     ASSERT((split & (PageSize() - 1)) == 0);
     FreeSubSegment(address(), split);
     region_.Subregion(region_, split, size() - split);
   }
   ASSERT(new_size <= size());
   FreeSubSegment(reinterpret_cast<void*>(start() + new_size),
                  size() - new_size);
   region_.Subregion(region_, 0, new_size);
 }
 
 }  // namespace dart