Reenable the tcmalloc SecurityTests in base_unittests on Windows

base/security_unittest.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ skipping 28 matching lines @@
   // more robust than merely using "volatile".
   __asm__ volatile ("" : "+r" (value));
 #endif  // __GNUC__
   return value;
 }
 
 // - NO_TCMALLOC (should be defined if we compile with linux_use_tcmalloc=0)
 // - ADDRESS_SANITIZER because it has its own memory allocator
 // - IOS does not use tcmalloc
 // - OS_MACOSX does not use tcmalloc
-// - OS_WIN does not use tcmalloc crbug.com/242304
 #if !defined(NO_TCMALLOC) && !defined(ADDRESS_SANITIZER) && \
-    !defined(OS_IOS) && !defined(OS_MACOSX) && !defined(OS_WIN)
+    !defined(OS_IOS) && !defined(OS_MACOSX)
   #define TCMALLOC_TEST(function) function
 #else
   #define TCMALLOC_TEST(function) DISABLED_##function
 #endif
 
 // TODO(jln): switch to std::numeric_limits<int>::max() when we switch to
 // C++11.
 const size_t kTooBigAllocSize = INT_MAX;
 
 // Detect runtime TCMalloc bypasses.
 bool IsTcMallocBypassed() {
 #if defined(OS_LINUX) || defined(OS_CHROMEOS)
   // This should detect a TCMalloc bypass from Valgrind.
   char* g_slice = getenv("G_SLICE");
   if (g_slice && !strcmp(g_slice, "always-malloc"))
     return true;
+#elif defined(OS_WIN)
+  // This should detect a TCMalloc bypass from setting
+  // the CHROME_ALLOCATOR environment variable.
+  char* allocator = getenv("CHROME_ALLOCATOR");
+  if (allocator && strcmp(allocator, "tcmalloc"))
+    return true;
 #endif
   return false;
 }
 
 bool CallocDiesOnOOM() {
 // The wrapper function in base/process_util_linux.cc that is used when we
 // compile without TCMalloc will just die on OOM instead of returning NULL.
 // This function is explicitly disabled if we compile with AddressSanitizer,
 // MemorySanitizer or ThreadSanitizer.
 #if defined(OS_LINUX) && defined(NO_TCMALLOC) && \
@@ skipping 214 matching lines @@
   // kRandomMask, so we use it as an additional detection mechanism.
   const uintptr_t kRandomMask = 0x3fffffffffffULL;
   bool impossible_random_address =
       reinterpret_cast<uintptr_t>(ptr.get()) & ~kRandomMask;
   EXPECT_FALSE(impossible_random_address);
 }
 
 #endif  // (defined(OS_LINUX) || defined(OS_CHROMEOS)) && defined(__x86_64__)
 
 }  // namespace