Updated analysis in videoprocessor.

- Run analysis after all frames are processed. Before part of it was
done at bitrate change points;
- Analysis is done for whole stream as well as for each rate update
interval;
- Changed units from number of frames to time units for some metrics
and thresholds. E.g. 'num frames to hit tagret bitrate' is changed to
'time to reach target bitrate, sec';
- Changed data type of FrameStatistic::max_nalu_length (renamed to
max_nalu_size_bytes) from rtc::Optional to size_t. There it no need to
use such advanced data type in such low level data structure.

Bug: webrtc:8524
Change-Id: Ic9f6eab5b15ee12a80324b1f9c101de1bf3c702f
Reviewed-on: https://webrtc-review.googlesource.com/31901
Commit-Queue: Sergey Silkin <ssilkin@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21653}

modules/video_coding/codecs/test/stats_unittest.cc

@@ -15,28 +15,21 @@
 namespace webrtc {
 namespace test {
 
-TEST(StatsTest, TestEmptyObject) {
-  Stats stats;
-  stats.PrintSummary();  // Should not crash.
-}
-
 TEST(StatsTest, AddSingleFrame) {
   Stats stats;
   FrameStatistic* frame_stat = stats.AddFrame();
-  EXPECT_EQ(0, frame_stat->frame_number);
+  EXPECT_EQ(0ull, frame_stat->frame_number);
   EXPECT_EQ(1u, stats.size());
 }
 
 TEST(StatsTest, AddMultipleFrames) {
   Stats stats;
-  const int kNumFrames = 1000;
-  for (int i = 0; i < kNumFrames; ++i) {
+  const size_t kNumFrames = 1000;
+  for (size_t i = 0; i < kNumFrames; ++i) {
     FrameStatistic* frame_stat = stats.AddFrame();
     EXPECT_EQ(i, frame_stat->frame_number);
   }
-  EXPECT_EQ(kNumFrames, static_cast<int>(stats.size()));
-
-  stats.PrintSummary();  // Should not crash.
+  EXPECT_EQ(kNumFrames, stats.size());
 }
 
 }  // namespace test