Fix the confict of declaration and definition between struct and class

This fixes the error when compiling with clang syntax checking
The error message was:
/update_engine/test_utils.h:188:1: error: 'ObjectFeederAction'
defined as a struct template here but previously declared as a
class template [-Werror,-Wmismatched-tags]

BUG=chromium:218781
TEST=USE="chrome_internal" CXXFLAGS="-clang -print-cmdline"
     CFLAGS="-clang -print-cmdline" emerge-x86-alex update_engine

Change-Id: Ieac9981c84c4e5779cbf876650f21a5d1b2acd72
Reviewed-on: https://gerrit.chromium.org/gerrit/47476
Reviewed-by: Jay Srinivasan <jaysri@chromium.org>
Tested-by: Yunlian Jiang <yunlian@chromium.org>
Commit-Queue: Yunlian Jiang <yunlian@chromium.org>
diff --git a/omaha_request_action.h b/omaha_request_action.h
index a75139e..528ce19 100644
--- a/omaha_request_action.h
+++ b/omaha_request_action.h
@@ -71,7 +71,7 @@
 
 class NoneType;
 class OmahaRequestAction;
-struct OmahaRequestParams;
+class OmahaRequestParams;
 class PrefsInterface;
 
 template<>