[LCP] regression tentative fix

This CL adds some optimization to do an early return when we know that
the PaintTimingDetectors are not going to do any work. This is the case
when the documentElement is visible and there is some opacity:0 (as
those paints are going to be ignored), as well as when the
documentElement is invisible and there is an opacity:0 depth higher than
1.

Bug: 1113723, 1113411, 1113067

Change-Id: If7a5a0224a89aa1da659b177da0d45d8dca30d57
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2360480Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799242}

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

@@ -137,6 +137,8 @@ void PaintTimingDetector::NotifyImagePaint(
     const ImageResourceContent* cached_image,
     const PropertyTreeStateOrAlias& current_paint_chunk_properties,
     const IntRect& image_border) {
+  if (IgnorePaintTimingScope::ShouldIgnore())
+    return;
   LocalFrameView* frame_view = object.GetFrameView();
   if (!frame_view)
     return;
@@ -153,6 +155,8 @@ void PaintTimingDetector::NotifyImagePaint(
 void PaintTimingDetector::NotifyImageFinished(
     const LayoutObject& object,
     const ImageResourceContent* cached_image) {
+  if (IgnorePaintTimingScope::ShouldIgnore())
+    return;
   if (image_paint_timing_detector_)
     image_paint_timing_detector_->NotifyImageFinished(object, cached_image);
 }

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

@@ -312,7 +312,7 @@ class ScopedPaintTimingDetectorBlockPaintHook {
 // static
 inline void PaintTimingDetector::NotifyTextPaint(
     const IntRect& text_visual_rect) {
-  if (IgnorePaintTimingScope::IgnoreDepth() > 1)
+  if (IgnorePaintTimingScope::ShouldIgnore())
     return;
   ScopedPaintTimingDetectorBlockPaintHook::AggregateTextPaint(text_visual_rect);
 }

third_party/blink/renderer/platform/graphics/paint/ignore_paint_timing_scope.h

@@ -35,6 +35,14 @@ class PLATFORM_EXPORT IgnorePaintTimingScope {
   static void IncrementIgnoreDepth() { ++ignore_depth_; }
   static int IgnoreDepth() { return ignore_depth_; }
 
+  // Used to bail out of paint timing algorithms when we know we won't track
+  // anything. We want to do this when a) document is visible but there is some
+  // opacity b) document is invisible but the depth is beyond 1.
+  static bool ShouldIgnore() {
+    return (!is_document_element_invisible_ && ignore_depth_) ||
+           ignore_depth_ > 1;
+  }
+
  private:
   base::AutoReset<int> reset_ignore_depth_;
   base::AutoReset<bool> reset_is_document_element_invisible_;