Delete unused methods of the VideoProcessing class. And fix a typo.

Rename EnableDenosing --> EnableDenoising.
Delete VideoProcessing FrameStats methods.
Delete VideoProcessingImpl::BrightnessDetection and related files.
Delete VideoProcessingImpl::Deflickering and related files.
Delete VideoProcessing::Brighten.

BUG=

Review URL: https://codereview.webrtc.org/1901393003

Cr-Commit-Position: refs/heads/master@{#12521}
diff --git a/webrtc/modules/video_processing/video_processing_impl.cc b/webrtc/modules/video_processing/video_processing_impl.cc
index cb52c67..b4f86ae 100644
--- a/webrtc/modules/video_processing/video_processing_impl.cc
+++ b/webrtc/modules/video_processing/video_processing_impl.cc
@@ -18,21 +18,6 @@
 
 namespace webrtc {
 
-namespace {
-
-int GetSubSamplingFactor(int width, int height) {
-  if (width * height >= 640 * 480) {
-    return 3;
-  } else if (width * height >= 352 * 288) {
-    return 2;
-  } else if (width * height >= 176 * 144) {
-    return 1;
-  } else {
-    return 0;
-  }
-}
-}  // namespace
-
 VideoProcessing* VideoProcessing::Create() {
   return new VideoProcessingImpl();
 }
@@ -40,83 +25,6 @@
 VideoProcessingImpl::VideoProcessingImpl() {}
 VideoProcessingImpl::~VideoProcessingImpl() {}
 
-void VideoProcessing::GetFrameStats(const VideoFrame& frame,
-                                    FrameStats* stats) {
-  ClearFrameStats(stats);  // The histogram needs to be zeroed out.
-  if (frame.IsZeroSize()) {
-    return;
-  }
-
-  int width = frame.width();
-  int height = frame.height();
-  stats->sub_sampling_factor = GetSubSamplingFactor(width, height);
-
-  const uint8_t* buffer = frame.buffer(kYPlane);
-  // Compute histogram and sum of frame
-  for (int i = 0; i < height; i += (1 << stats->sub_sampling_factor)) {
-    int k = i * width;
-    for (int j = 0; j < width; j += (1 << stats->sub_sampling_factor)) {
-      stats->hist[buffer[k + j]]++;
-      stats->sum += buffer[k + j];
-    }
-  }
-
-  stats->num_pixels = (width * height) / ((1 << stats->sub_sampling_factor) *
-                                          (1 << stats->sub_sampling_factor));
-  assert(stats->num_pixels > 0);
-
-  // Compute mean value of frame
-  stats->mean = stats->sum / stats->num_pixels;
-}
-
-bool VideoProcessing::ValidFrameStats(const FrameStats& stats) {
-  if (stats.num_pixels == 0) {
-    LOG(LS_WARNING) << "Invalid frame stats.";
-    return false;
-  }
-  return true;
-}
-
-void VideoProcessing::ClearFrameStats(FrameStats* stats) {
-  stats->mean = 0;
-  stats->sum = 0;
-  stats->num_pixels = 0;
-  stats->sub_sampling_factor = 0;
-  memset(stats->hist, 0, sizeof(stats->hist));
-}
-
-void VideoProcessing::Brighten(int delta, VideoFrame* frame) {
-  RTC_DCHECK(!frame->IsZeroSize());
-  RTC_DCHECK(frame->width() > 0);
-  RTC_DCHECK(frame->height() > 0);
-
-  int num_pixels = frame->width() * frame->height();
-
-  int look_up[256];
-  for (int i = 0; i < 256; i++) {
-    int val = i + delta;
-    look_up[i] = ((((val < 0) ? 0 : val) > 255) ? 255 : val);
-  }
-
-  uint8_t* temp_ptr = frame->buffer(kYPlane);
-  for (int i = 0; i < num_pixels; i++) {
-    *temp_ptr = static_cast<uint8_t>(look_up[*temp_ptr]);
-    temp_ptr++;
-  }
-}
-
-int32_t VideoProcessingImpl::Deflickering(VideoFrame* frame,
-                                          FrameStats* stats) {
-  rtc::CritScope mutex(&mutex_);
-  return deflickering_.ProcessFrame(frame, stats);
-}
-
-int32_t VideoProcessingImpl::BrightnessDetection(const VideoFrame& frame,
-                                                 const FrameStats& stats) {
-  rtc::CritScope mutex(&mutex_);
-  return brightness_detection_.ProcessFrame(frame, stats);
-}
-
 void VideoProcessingImpl::EnableTemporalDecimation(bool enable) {
   rtc::CritScope mutex(&mutex_);
   frame_pre_processor_.EnableTemporalDecimation(enable);
@@ -150,9 +58,9 @@
   return frame_pre_processor_.GetDecimatedHeight();
 }
 
-void VideoProcessingImpl::EnableDenosing(bool enable) {
+void VideoProcessingImpl::EnableDenoising(bool enable) {
   rtc::CritScope cs(&mutex_);
-  frame_pre_processor_.EnableDenosing(enable);
+  frame_pre_processor_.EnableDenoising(enable);
 }
 
 const VideoFrame* VideoProcessingImpl::PreprocessFrame(