simpleperf: add symbol defore demangle in protobuf interface.

Bug: none
Test: run simpleperf_unit_test.

Change-Id: I55ce099bea257c25b2617de98ce714510e5abb9e
diff --git a/simpleperf/report_sample.proto b/simpleperf/report_sample.proto
index 1a4886e..bbe46fb 100644
--- a/simpleperf/report_sample.proto
+++ b/simpleperf/report_sample.proto
@@ -69,6 +69,9 @@
 
   // symbol table of the file.
   repeated string symbol = 3;
+
+  // mangled symbol table of the file.
+  repeated string mangled_symbol = 4;
 }
 
 message Thread {