Add an option to disable native stack dumping on SIGQUIT.

Some of our (stress) run-tests do ANR dumping, which end up
stressing libunwind, that has known problems. To avoid getting
flakes due to libunwind, disable native stack dumping on SIGQUIT
for our run-tests.

bug:27185632
bug:24664297
Change-Id: I69085e48db903d6240448d71666ae2dcd091922e
diff --git a/runtime/runtime.h b/runtime/runtime.h
index bec26f8..1956bae 100644
--- a/runtime/runtime.h
+++ b/runtime/runtime.h
@@ -603,6 +603,10 @@
     safe_mode_ = mode;
   }
 
+  bool GetDumpNativeStackOnSigQuit() const {
+    return dump_native_stack_on_sig_quit_;
+  }
+
  private:
   static void InitPlatformSignalHandlers();
 
@@ -813,6 +817,9 @@
   // Whether the application should run in safe mode, that is, interpreter only.
   bool safe_mode_;
 
+  // Whether threads should dump their native stack on SIGQUIT.
+  bool dump_native_stack_on_sig_quit_;
+
   DISALLOW_COPY_AND_ASSIGN(Runtime);
 };
 std::ostream& operator<<(std::ostream& os, const Runtime::CalleeSaveType& rhs);