Handle empty records in records_manager_'s queue properly

Update ImagePaintTimingDetector's last_registered_frame_index_ acordingly when empty records are removed from the records_manager_'s queue.

Bug: 1062974
Change-Id: I2e5923eb070249d6c561a4bac4defbf9345e5f72
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2108732Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756840}

AUTHORS

@@ -1004,6 +1004,7 @@ Vitaliy Kharin <kvserr@gmail.com>
 Vivek Galatage <vivek.vg@samsung.com>
 Volker Sorge <volker.sorge@gmail.com>
 Waihung Fu <fufranci@amazon.com>
+Wojciech Bielawski <wojciech.bielawski@gmail.com>
 Wanming Lin <wanming.lin@intel.com>
 Wei Li <wei.c.li@intel.com>
 Wenxiang Qian <leonwxqian@gmail.com>

third_party/blink/renderer/core/paint/image_paint_timing_detector.cc

@@ -142,11 +142,11 @@ void ImagePaintTimingDetector::OnPaintFinished() {
         .UpdateLargestContentfulPaintCandidate();
   }
 
-  if (!records_manager_.HasUnregisteredRecordsInQueued(
+  if (!records_manager_.HasUnregisteredRecordsInQueue(
           last_registered_frame_index_))
     return;
 
-  last_registered_frame_index_ = records_manager_.LastQueuedFrameIndex();
+  last_registered_frame_index_ = frame_index_ - 1;
   RegisterNotifySwapTime();
 }
 

third_party/blink/renderer/core/paint/image_paint_timing_detector.h

@@ -122,7 +122,7 @@ class CORE_EXPORT ImageRecordsManager {
 
   // Compare the last frame index in queue with the last frame index that has
   // registered for assigning paint time.
-  inline bool HasUnregisteredRecordsInQueued(
+  inline bool HasUnregisteredRecordsInQueue(
       unsigned last_registered_frame_index) {
     while (!images_queued_for_paint_time_.IsEmpty() &&
            !images_queued_for_paint_time_.back()) {
@@ -130,7 +130,6 @@ class CORE_EXPORT ImageRecordsManager {
     }
     if (images_queued_for_paint_time_.IsEmpty())
       return false;
-    DCHECK(last_registered_frame_index <= LastQueuedFrameIndex());
     return last_registered_frame_index < LastQueuedFrameIndex();
   }
   void AssignPaintTimeToRegisteredQueuedRecords(