Frames started after FCP will be submitted to frame_sorter

Frames which are started prior to first contentful paint will not be added to frame_sorter and as a result would not be reported as part of normalized smoothness metrics.

Bug: 1157479
Change-Id: I665172b297c38ada0e2d468417342e5c2df06374
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2584647Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Behdad Bakhshinategh <behdadb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836278}

cc/metrics/dropped_frame_counter.cc

@@ -85,7 +85,8 @@ void DroppedFrameCounter::ResetFrameSorter() {
 }
 
 void DroppedFrameCounter::OnBeginFrame(const viz::BeginFrameArgs& args) {
-  frame_sorter_.AddNewFrame(args);
+  if (fcp_received_)
+    frame_sorter_.AddNewFrame(args);
 }
 
 void DroppedFrameCounter::OnEndFrame(const viz::BeginFrameArgs& args,
@@ -95,7 +96,9 @@ void DroppedFrameCounter::OnEndFrame(const viz::BeginFrameArgs& args,
       ++total_smoothness_dropped_;
     ReportFrames();
   }
-  frame_sorter_.AddFrameResult(args, is_dropped);
+
+  if (fcp_received_)
+    frame_sorter_.AddFrameResult(args, is_dropped);
 }
 
 void DroppedFrameCounter::ReportFrames() {

cc/metrics/dropped_frame_counter_unittest.cc

@@ -254,6 +254,7 @@ class DroppedFrameCounterTest : public testing::Test {
  public:
   DroppedFrameCounterTest() {
     dropped_frame_counter_.set_total_counter(&total_frame_counter_);
+    dropped_frame_counter_.OnFcpReceived();
   }
   ~DroppedFrameCounterTest() override = default;