Add offset to map data.

Also, print the offset in the maps section.

Bug: 20864928
Change-Id: I71f005726e5ef73cf75bbcb8f829fd5127cb9d61
(cherry picked from commit 5c8856854de4ae7836fc1073d534f4b7b7a03eb9)
diff --git a/include/backtrace/BacktraceMap.h b/include/backtrace/BacktraceMap.h
index 731c248..784bc03 100644
--- a/include/backtrace/BacktraceMap.h
+++ b/include/backtrace/BacktraceMap.h
@@ -37,6 +37,7 @@
 
   uintptr_t start;
   uintptr_t end;
+  uintptr_t offset;
   uintptr_t load_base;
   int flags;
   std::string name;