[windows] Revert virtual memory changes

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 17 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 (embedder_allocated()) {
+  if (embedder_allocated() || (reserved_size_ == 0)) {
     return;
   }
   if (VirtualFree(address(), 0, MEM_RELEASE) == 0) {
-    FATAL1("VirtualFree failed: Error code %d\n", GetLastError());
+    FATAL("VirtualFree failed");
   }
 }
 
 
 bool VirtualMemory::FreeSubSegment(void* address, intptr_t size) {
-  if (VirtualFree(address, size, MEM_DECOMMIT) == 0) {
-    FATAL1("VirtualFree failed: Error code %d\n", GetLastError());
-  }
-  return true;
+  // On Windows only the entire segment returned by VirtualAlloc
+  // can be freed. Therefore we will have to waste these unused
+  // virtual memory sub-segments.
+  return false;
 }
 
 
 bool VirtualMemory::Commit(uword addr, intptr_t size, bool executable) {
   ASSERT(Contains(addr));
   ASSERT(Contains(addr + size) || (addr + size == end()));
   int prot = executable ? PAGE_EXECUTE_READWRITE : PAGE_READWRITE;
   if (VirtualAlloc(reinterpret_cast<void*>(addr), size, MEM_COMMIT, prot) ==
       NULL) {
     return false;
@@ skipping 30 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)