Add end() method to bionic's ScopedTrace class

Bug: http://b/27195126
Test: make
Change-Id: I8243629200606ca87b11cbd479ca093add42eb56
diff --git a/libc/private/bionic_systrace.h b/libc/private/bionic_systrace.h
index 0b4560f..304fb80 100644
--- a/libc/private/bionic_systrace.h
+++ b/libc/private/bionic_systrace.h
@@ -28,8 +28,13 @@
   explicit ScopedTrace(const char* message);
   ~ScopedTrace();
 
+  void End();
  private:
+  bool called_end_;
   DISALLOW_COPY_AND_ASSIGN(ScopedTrace);
 };
 
+void bionic_trace_begin(const char* message);
+void bionic_trace_end();
+
 #endif