GTTF: Make Linux stack dump signal handler async-signal safe.

base/debug/stack_trace.h

Index: base/debug/stack_trace.h
diff --git a/base/debug/stack_trace.h b/base/debug/stack_trace.h
index 60d5821a7094293ad576bee730ed0569759c5272..4da065bb55220b5a23f7e95cf05de31c2b9431db 100644
--- a/base/debug/stack_trace.h
+++ b/base/debug/stack_trace.h
@@ -73,6 +73,20 @@ class BASE_EXPORT StackTrace {
   size_t count_;
 };
 
+namespace internal {
+
+#if defined(OS_POSIX) && !defined(OS_ANDROID) && !defined(OS_IOS)
+// POSIX doesn't define any async-signal safe function for converting
+// an integer to ASCII. We'll have to define our own version.
+// itoa_r() converts a (signed) integer to ASCII. It returns "buf", if the
+// conversion was successful or NULL otherwise. It never writes more than "sz"
+// bytes. Output will be truncated as needed, and a NUL character is always
+// appended.
+BASE_EXPORT char *itoa_r(intptr_t i, char *buf, size_t sz, int base);
+#endif  // defined(OS_POSIX) && !defined(OS_ANDROID) && !defined(OS_IOS)
+
+}  // namespace internal
+
 }  // namespace debug
 }  // namespace base