Added Reset method to TwopassStatsStore

The stats buffer needs to be reset between runs of the
encoder. I added a Reset() function to TwopassStatsStore
and called it at the beginning of each encode.

This enables us to run multiple encodes which was
previously not possible since there was no way to reset
the stats between runs.

Change-Id: Iebb18dab83ba9331f009f764cc858609738a27f9

test/encode_test_driver.cc

@@ -126,6 +126,9 @@ void EncoderTest::RunLoop(VideoSource *video) {
 #if CONFIG_VP8_DECODER
   vpx_codec_dec_cfg_t dec_cfg = {0};
 #endif
+
+  stats_.Reset();
+
   for (unsigned int pass = 0; pass < passes_; pass++) {
     last_pts_ = 0;
 

test/encode_test_driver.h

@@ -65,6 +65,10 @@ class TwopassStatsStore {
     return buf;
   }
 
+  void Reset() {
+    buffer_.clear();
+  }
+
  protected:
   std::string  buffer_;
 };