Skipped compositor frames (over 100) would not be submitted as dropped frames

Submitting a bulk of skipped compositor frames as dropped frames can affect the normalized worst case percent dropped frames. This change stops submitting skipped frames more than the limit (100 frames).

Bug: 1157101
Change-Id: I63c6f57c9d6c7fa2021842f13f1ca86ff7c9fd48
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2583008Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Behdad Bakhshinategh <behdadb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836279}

cc/metrics/compositor_frame_reporting_controller.cc

@@ -489,9 +489,13 @@ void CompositorFrameReportingController::CreateReportersForDroppedFrames(
 
   // Up to 100 frames will be reported (100 closest frames to new_args).
   const uint32_t kMaxFrameCount = 100;
-  uint32_t index = (interval > kMaxFrameCount) ? interval - kMaxFrameCount : 1;
-  auto timestamp = old_args.frame_time + (old_args.interval * index);
-  for (uint32_t i = index; i < interval; ++i, timestamp += old_args.interval) {
+
+  // If there are more than 100 frames skipped, ignore them
+  if (interval > kMaxFrameCount)
+    return;
+
+  auto timestamp = old_args.frame_time + old_args.interval;
+  for (uint32_t i = 1; i < interval; ++i, timestamp += old_args.interval) {
     auto args = viz::BeginFrameArgs::Create(
         BEGINFRAME_FROM_HERE, old_args.frame_id.source_id,
         old_args.frame_id.sequence_number + i, timestamp,

cc/metrics/compositor_frame_reporting_controller_unittest.cc

@@ -1462,10 +1462,10 @@ TEST_F(CompositorFrameReportingControllerTest,
   EXPECT_EQ(0u, dropped_counter.total_main_dropped());
   EXPECT_EQ(0u, dropped_counter.total_compositor_dropped());
 
-  // Now skip over a 200 frames (100 skipped frames should be added)
+  // Now skip over a 101 frames (It should be ignored as it more than 100)
   // and submit + present another frame.
-  const uint32_t kSkipFrames = 200;
-  const uint32_t kSkipFramesActual = std::min(kSkipFrames, 100u);
+  const uint32_t kSkipFrames = 101;
+  const uint32_t kSkipFramesActual = 0;
   for (uint32_t i = 0; i < kSkipFrames; ++i)
     IncrementCurrentId();
   SimulatePresentCompositorFrame();