Add offset for native stack dump.

When dumping the stack from a shared library loaded out of an apk,
the art stack dumper didn't match the backtrace unwinding code and
include an offset. Add that back in so that this backtrace can be
passed to go/as.

Test: Loaded an app with a shared library from an apk and did a kill -3.
Test: Observed that the offset value is set properly.
Change-Id: I881946330e76b9aab28cf7dbd94fe406bac7895a
diff --git a/runtime/native_stack_dump.cc b/runtime/native_stack_dump.cc
index 099d77e..4d4bab7 100644
--- a/runtime/native_stack_dump.cc
+++ b/runtime/native_stack_dump.cc
@@ -345,6 +345,9 @@
       } else {
         os << it->map.name;
       }
+      if (it->map.offset != 0) {
+        os << StringPrintf(" (offset %" PRIx64 ")", it->map.offset);
+      }
       os << " (";
       if (!it->func_name.empty()) {
         os << it->func_name;