Refactor VideoDenoiser to use a buffer pool, replacing explicit double buffering.

webrtc/modules/video_processing/frame_preprocessor.cc

Index: webrtc/modules/video_processing/frame_preprocessor.cc
diff --git a/webrtc/modules/video_processing/frame_preprocessor.cc b/webrtc/modules/video_processing/frame_preprocessor.cc
index e86bbbb3bf931d829596bbfc8c726bf9b246bff3..8d6d8bbaa6ef41c55997ec9b2c557e4f06970677 100644
--- a/webrtc/modules/video_processing/frame_preprocessor.cc
+++ b/webrtc/modules/video_processing/frame_preprocessor.cc
@@ -19,7 +19,6 @@ VPMFramePreprocessor::VPMFramePreprocessor()
   spatial_resampler_ = new VPMSimpleSpatialResampler();
   vd_ = new VPMVideoDecimator();
   EnableDenoising(false);
-  denoised_frame_toggle_ = 0;
 }
 
 VPMFramePreprocessor::~VPMFramePreprocessor() {
@@ -96,22 +95,10 @@ const VideoFrame* VPMFramePreprocessor::PreprocessFrame(
 
   const VideoFrame* current_frame = &frame;
   if (denoiser_) {
-    rtc::scoped_refptr<I420Buffer>* denoised_buffer = &denoised_buffer_[0];
-    rtc::scoped_refptr<I420Buffer>* denoised_buffer_prev = &denoised_buffer_[1];
-    // Swap the buffer to save one memcpy in DenoiseFrame.
-    if (denoised_frame_toggle_) {
-      denoised_buffer = &denoised_buffer_[1];
-      denoised_buffer_prev = &denoised_buffer_[0];
-    }
-    // Invert the flag.
-    denoised_frame_toggle_ ^= 1;
-    denoiser_->DenoiseFrame(current_frame->video_frame_buffer(),
-                            denoised_buffer,
-                            denoised_buffer_prev, true);
-    denoised_frame_ = VideoFrame(*denoised_buffer,
-                                 current_frame->timestamp(),
-                                 current_frame->render_time_ms(),
-                                 current_frame->rotation());
+    denoised_frame_ = VideoFrame(
+        denoiser_->DenoiseFrame(current_frame->video_frame_buffer(), true),
+        current_frame->timestamp(), current_frame->render_time_ms(),
+        current_frame->rotation());
     current_frame = &denoised_frame_;
   }