Discards frames for code within library.

When doing a local unwind, do not include the frames that come
from either libunwind or libbacktrace.

Bug: 11518609
Change-Id: I0ec8d823aebbfa0903e61b16b7e5663f3fd65e78
diff --git a/libbacktrace/BacktraceCurrent.h b/libbacktrace/BacktraceCurrent.h
index 81ea81d..8aad36d 100644
--- a/libbacktrace/BacktraceCurrent.h
+++ b/libbacktrace/BacktraceCurrent.h
@@ -46,6 +46,9 @@
 
   bool Unwind(size_t num_ignore_frames, ucontext_t* ucontext) override;
 
+protected:
+  bool DiscardFrame(const backtrace_frame_data_t& frame);
+
 private:
   bool UnwindThread(size_t num_ignore_frames);