Add DwarfSection classes.

Bug: 23762183

Test: Ran new unit tests.
Change-Id: Icca2a73c50d467718ba4ac41e1c8f541488620dd
diff --git a/libunwindstack/DwarfError.h b/libunwindstack/DwarfError.h
index 824c307..c00f17d 100644
--- a/libunwindstack/DwarfError.h
+++ b/libunwindstack/DwarfError.h
@@ -27,6 +27,8 @@
   DWARF_ERROR_STACK_INDEX_NOT_VALID,
   DWARF_ERROR_NOT_IMPLEMENTED,
   DWARF_ERROR_TOO_MANY_ITERATIONS,
+  DWARF_ERROR_CFA_NOT_DEFINED,
+  DWARF_ERROR_UNSUPPORTED_VERSION,
 };
 
 #endif  // _LIBUNWINDSTACK_DWARF_ERROR_H