[cc] facilitate use of BeginFrameAcks in tests.

cc/test/begin_frame_args_test.h

Index: cc/test/begin_frame_args_test.h
diff --git a/cc/test/begin_frame_args_test.h b/cc/test/begin_frame_args_test.h
index 57cee81fd0bcb535f868ca95477b6c18ac6373e3..5d5998264243b5f4f7797f256dfd16ca030db6b8 100644
--- a/cc/test/begin_frame_args_test.h
+++ b/cc/test/begin_frame_args_test.h
@@ -62,6 +62,13 @@ bool operator==(const BeginFrameArgs& lhs, const BeginFrameArgs& rhs);
 ::std::ostream& operator<<(::std::ostream& os, const BeginFrameArgs& args);
 void PrintTo(const BeginFrameArgs& args, ::std::ostream* os);
 
+// Allow "EXPECT_EQ(ack1, ack2);"
+bool operator==(const BeginFrameAck& lhs, const BeginFrameAck& rhs);
+
+// Allow gtest to pretty print BeginFrameAcks.
+::std::ostream& operator<<(::std::ostream& os, const BeginFrameAck& ack);
+void PrintTo(const BeginFrameAck& ack, ::std::ostream* os);
+
 }  // namespace cc
 
 #endif  // CC_TEST_BEGIN_FRAME_ARGS_TEST_H_