Abort: change the magic value written to NULL

Make sure that the magic value can be cast to a char properly.

BUG=724399,b:70905156

Review URL: https://chromiumcodereview.appspot.com/10541122

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@141814 0039d316-1c4b-4281-b951-d872f2087c98
(cherry picked from commit b9ccf65a)
Signed-off-by: Gabriel Marin <gmx@chromium.org>

Change-Id: I31162aefe53624f4bc61a6b2bc6fe83f9df5ff68
Reviewed-on: https://chromium-review.googlesource.com/1130779Reviewed-by: Will Harris <wfh@chromium.org>
Commit-Queue: Gabriel Marin <gmx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578736}

third_party/tcmalloc/chromium/src/base/abort.cc

@@ -12,7 +12,7 @@ namespace tcmalloc {
 ATTRIBUTE_NOINLINE void Abort() {
   // Make a segmentation fault to force abort. Writing to a specific address
   // so it's easier to find on crash stacks.
-  *(reinterpret_cast<volatile char*>(NULL) + 57) = 0x2001;
+  *(reinterpret_cast<volatile char*>(NULL) + 57) = 0x21;
 }
 
 } // namespace tcmalloc