Only set memory tool define if not set.

xfa/fgas/crt/fgas_memory.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "xfa/fgas/crt/fgas_memory.h"
 
+#ifndef MEMORY_TOOL_REPLACES_ALLOCATOR
 #define MEMORY_TOOL_REPLACES_ALLOCATOR  // Temporary, for CF testing.
+#endif
 
 #include <algorithm>
 
 #ifdef MEMORY_TOOL_REPLACES_ALLOCATOR
 
 namespace {
 
 class CFX_DefStore : public IFX_MemoryAllocator, public CFX_Target {
  public:
   CFX_DefStore() {}
@@ skipping 220 matching lines @@
   }
 }
 size_t CFX_FixedStore::SetDefChunkSize(size_t iChunkSize) {
   ASSERT(iChunkSize != 0);
   size_t v = m_iDefChunkSize;
   m_iDefChunkSize = FX_4BYTEALIGN(iChunkSize);
   return v;
 }
 
 #endif  // MEMORY_TOOL_REPLACES_ALLOCATOR