Fix -INT_MIN integer overflow in itoa_r().

base/debug/stack_trace_posix.cc

 // Copyright (c) 2012 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 "base/debug/stack_trace.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <signal.h>
 #include <stdio.h>
@@ skipping 766 matching lines @@
     buf[0] = '\000';
     return NULL;
   }
 
   char *start = buf;
 
   uintptr_t j = i;
 
   // Handle negative numbers (only for base 10).
   if (i < 0 && base == 10) {
-    j = -i;
+    // This does "j = -i" while avoiding integer overflow.
+    j = static_cast<uintptr_t>(-(i + 1)) + 1;
 
     // Make sure we can write the '-' character.
     if (++n > sz) {
       buf[0] = '\000';
       return NULL;
     }
     *start++ = '-';
   }
 
   // Loop until we have converted the entire number. Output at least one
@@ skipping 26 matching lines @@
     *ptr = *start;
     *start++ = ch;
   }
   return buf;
 }
 
 }  // namespace internal
 
 }  // namespace debug
 }  // namespace base