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/test_utils.h b/test_utils.h
index 8305c14..30f1f89 100644
--- a/test_utils.h
+++ b/test_utils.h
@@ -185,7 +185,7 @@
 // This is a simple Action class for testing. It feeds an object into
 // another action.
 template<typename T>
-struct ObjectFeederAction : public Action<ObjectFeederAction<T> > {
+class ObjectFeederAction : public Action<ObjectFeederAction<T> > {
  public:
   typedef NoneType InputObjectType;
   typedef T OutputObjectType;
@@ -219,7 +219,7 @@
 // This is a simple Action class for testing. It receives an object from
 // another action.
 template<typename T>
-struct ObjectCollectorAction : public Action<ObjectCollectorAction<T> > {
+class ObjectCollectorAction : public Action<ObjectCollectorAction<T> > {
  public:
   typedef T InputObjectType;
   typedef NoneType OutputObjectType;