AU: Extent writer utility classes

src/platform/update_engine/test_utils.h

Index: src/platform/update_engine/test_utils.h
diff --git a/src/platform/update_engine/test_utils.h b/src/platform/update_engine/test_utils.h
index cd17ec1fdf52f92289b08d012b6ae2a0dc1f0a1d..bba3ed1b68215729893fb5db046f3a19d39f048f 100644
--- a/src/platform/update_engine/test_utils.h
+++ b/src/platform/update_engine/test_utils.h
@@ -44,6 +44,8 @@ inline int System(const std::string& cmd) {
   return system(cmd.c_str());
 }
 
+void FillWithData(std::vector<char>* buffer);
+
 namespace {
 // 300 byte pseudo-random string. Not null terminated.
 // This does not gzip compress well.