Added handler for PSNR packets to EncoderTest class

Added a virtual function to handle PSNR packets.

Change-Id: Id2a6372c691a14f19bbeed217a93a9df03e81e75
diff --git a/test/encode_test_driver.h b/test/encode_test_driver.h
index 7b95a8d..0141fa9 100644
--- a/test/encode_test_driver.h
+++ b/test/encode_test_driver.h
@@ -176,6 +176,9 @@
   // Hook to be called on every compressed data packet.
   virtual void FramePktHook(const vpx_codec_cx_pkt_t *pkt) {}
 
+  // Hook to be called on every PSNR packet.
+  virtual void PSNRPktHook(const vpx_codec_cx_pkt_t *pkt) {}
+
   // Hook to determine whether the encode loop should continue.
   virtual bool Continue() const { return !abort_; }