Split AddLatencyInFrame into 2 methods.

AverageLagTracker::AddLatencyInFrame is already logically splited
(most part of its body is inside an if/else body) into 2 cases:
ScrollBegin and ScrollUpdate. This CL aims to create a method
for each case so AddLatencyInFrame is leaner and simpler to read.

Also, as this class in being refactored at
https://chromium-review.googlesource.com/c/chromium/src/+/2189633
this simple refactor will reduce the amount of noise created by
CL #2189633.


Bug: 1079024, 1079028
Change-Id: I7c9d2567ac3a875ca4c03b33d77a7a169bbb6375
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2216707Reviewed-by: David Bokan <bokan@chromium.org>
Reviewed-by: Navid Zolghadr <nzolghadr@chromium.org>
Reviewed-by: Daniel Libby <dlibby@microsoft.com>
Commit-Queue: João Victor Almeida de Aguiar <joalmei@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#774708}

ui/latency/average_lag_tracker.cc

@@ -26,6 +26,20 @@ void AverageLagTracker::AddLatencyInFrame(
     return;
 
   if (scroll_name == "ScrollBegin") {
+    AddScrollBeginInFrame(gpu_swap_begin_timestamp, event_timestamp);
+  } else if (scroll_name == "ScrollUpdate" &&
+             !last_event_timestamp_.is_null()) {
+    AddScrollUpdateInFrame(latency, gpu_swap_begin_timestamp, event_timestamp);
+  }
+
+  last_event_timestamp_ = event_timestamp;
+  last_event_accumulated_delta_ += latency.scroll_update_delta();
+  last_rendered_accumulated_delta_ += latency.predicted_scroll_update_delta();
+}
+
+void AverageLagTracker::AddScrollBeginInFrame(
+    base::TimeTicks gpu_swap_begin_timestamp,
+    base::TimeTicks event_timestamp) {
   // Flush all unfinished frames.
   while (!frame_lag_infos_.empty()) {
     frame_lag_infos_.front().lag_area += LagForUnfinishedFrame(
@@ -49,8 +63,12 @@ void AverageLagTracker::AddLatencyInFrame(
   last_event_accumulated_delta_ = 0;
   last_rendered_accumulated_delta_ = 0;
   is_begin_ = true;
-  } else if (scroll_name == "ScrollUpdate" &&
-             !last_event_timestamp_.is_null()) {
+}
+
+void AverageLagTracker::AddScrollUpdateInFrame(
+    const LatencyInfo& latency,
+    base::TimeTicks gpu_swap_begin_timestamp,
+    base::TimeTicks event_timestamp) {
   // Only accept events in nondecreasing order.
   if ((event_timestamp - last_event_timestamp_).InMilliseconds() < 0)
     return;
@@ -98,11 +116,6 @@ void AverageLagTracker::AddLatencyInFrame(
         front_time, back_time, latency, event_timestamp,
         frame_lag_infos_.front().rendered_accumulated_delta_no_prediction);
   }
-  }
-
-  last_event_timestamp_ = event_timestamp;
-  last_event_accumulated_delta_ += latency.scroll_update_delta();
-  last_rendered_accumulated_delta_ += latency.predicted_scroll_update_delta();
 }
 
 float AverageLagTracker::LagBetween(base::TimeTicks front_time,

ui/latency/average_lag_tracker.h

@@ -50,6 +50,12 @@ class AverageLagTracker {
     float lag_area_no_prediction;
   } LagAreaInFrame;
 
+  void AddScrollBeginInFrame(base::TimeTicks gpu_swap_begin_timestamp,
+                             base::TimeTicks event_timestamp);
+  void AddScrollUpdateInFrame(const LatencyInfo& latency,
+                              base::TimeTicks gpu_swap_begin_timestamp,
+                              base::TimeTicks event_timestamp);
+
   // Calculate lag in 1 seconds intervals and report UMA.
   void CalculateAndReportAverageLagUma(bool send_anyway = false);