Force crash on Mac10.9- in BreakDebugger()

base/debug/stack_trace_posix.cc

Index: base/debug/stack_trace_posix.cc
diff --git a/base/debug/stack_trace_posix.cc b/base/debug/stack_trace_posix.cc
index 27a656e6caffe7a3efc58fda7c4758b5d7fcdf77..99f40e986e56abf4c0cb724d18d882ca722ade57 100644
--- a/base/debug/stack_trace_posix.cc
+++ b/base/debug/stack_trace_posix.cc
@@ -374,8 +374,8 @@ void StackDumpSignalHandler(int signal, siginfo_t* info, void* void_context) {
   PrintToStderr("[end of stack trace]\n");
 
 #if defined(OS_MACOSX) && !defined(OS_IOS)
-  if (::signal(signal, SIG_DFL) == SIG_ERR)

[dcheng, 2016/09/09 05:15:50]

Why is this change necessary as well?

[Xianzhu, 2016/09/09 05:20:13]

Without this, the forced crash will be ignored.

At least on Mac10.9, ::signal(signal, SIG_DFL) seems to just restore the
original signal handler but not to reraise the signal. Based on my test, if
::signal(signal, SIG_DFL) is successful, this function just returns, and nothing
happens. _exit(1) will let the program crash. 

-    _exit(1);
+  ::signal(signal, SIG_DFL);
+  _exit(1);
 #else
   // Non-Mac OSes should probably reraise the signal as well, but the Linux
   // sandbox tests break on CrOS devices.