Add pre decode frame hook to decoder test class.

Adds a hook that derived test classes can implement to be notified
before every call to decode a frame.

Change-Id: Iefa836459cf3e5d7df9ee27f8198daf82b1be088

test/decode_test_driver.cc

@@ -30,6 +30,7 @@ void DecoderTest::RunLoop(CompressedVideoSource *video) {
 
   // Decode frames.
   for (video->Begin(); video->cxdata(); video->Next()) {
+    PreDecodeFrameHook(*video, decoder);
     vpx_codec_err_t res_dec = decoder->DecodeFrame(video->cxdata(),
                                                    video->frame_size());
     ASSERT_EQ(VPX_CODEC_OK, res_dec) << decoder->DecodeError();

test/decode_test_driver.h

@@ -101,6 +101,10 @@ class DecoderTest {
   // Main decoding loop
   virtual void RunLoop(CompressedVideoSource *video);
 
+  // Hook to be called before decompressing every frame.
+  virtual void PreDecodeFrameHook(const CompressedVideoSource& video,
+                                  Decoder *decoder) {}
+
   // Hook to be called on every decompressed frame.
   virtual void DecompressedFrameHook(const vpx_image_t& img,
                                      const unsigned int frame_number) {}