[PE] Make NeedsOverflowControlsClip() more accurate

Previously the function was a static function which didn't know the
current paint offset so was unable to calculate the accurate pixel
snapped border box rect, so used a conservative border box rect which
caused some unnecessary OverflowControlsClip() whose change of
existence was not updated.

Now make it a method of FragmentPaintPropertyTreeBuilder to return
the accurate needs, so the change of needs is covered by existing
SetNeedsPaintPropertyTreeUpdate conditions.

Bug: 823935
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I07578033d202af3c996004a88f25711eaac245a2
Reviewed-on: https://chromium-review.googlesource.com/974167Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544870}

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp

@@ -339,6 +339,7 @@ class FragmentPaintPropertyTreeBuilder {
   ALWAYS_INLINE void UpdateCssClip();
   ALWAYS_INLINE void UpdateClipPathClip(bool spv1_compositing_specific_pass);
   ALWAYS_INLINE void UpdateLocalBorderBoxContext();
+  ALWAYS_INLINE bool NeedsOverflowControlsClip() const;
   ALWAYS_INLINE void UpdateOverflowControlsClip();
   ALWAYS_INLINE void UpdateInnerBorderRadiusClip();
   ALWAYS_INLINE void UpdateOverflowClip();
@@ -1047,11 +1048,11 @@ static bool NeedsOverflowClip(const LayoutObject& object) {
          !IsPrintingRootLayoutView(object);
 }
 
-static bool NeedsOverflowControlsClip(const LayoutObject& object) {
-  if (!object.HasOverflowClip())
+bool FragmentPaintPropertyTreeBuilder::NeedsOverflowControlsClip() const {
+  if (!object_.HasOverflowClip())
     return false;
 
-  const auto& box = ToLayoutBox(object);
+  const auto& box = ToLayoutBox(object_);
   const auto* scrollable_area = box.GetScrollableArea();
   IntRect scroll_controls_bounds =
       scrollable_area->ScrollCornerAndResizerRect();
@@ -1059,8 +1060,10 @@ static bool NeedsOverflowControlsClip(const LayoutObject& object) {
     scroll_controls_bounds.Unite(scrollbar->FrameRect());
   if (const auto* scrollbar = scrollable_area->VerticalScrollbar())
     scroll_controls_bounds.Unite(scrollbar->FrameRect());
-  IntRect conservative_border_box_rect(IntPoint(), FlooredIntSize(box.Size()));
-  return !conservative_border_box_rect.Contains(scroll_controls_bounds);
+  auto pixel_snapped_border_box_rect = box.PixelSnappedBorderBoxRect(
+      ToLayoutSize(context_.current.paint_offset));
+  pixel_snapped_border_box_rect.SetLocation(IntPoint());
+  return !pixel_snapped_border_box_rect.Contains(scroll_controls_bounds);
 }
 
 static bool NeedsInnerBorderRadiusClip(const LayoutObject& object) {
@@ -1101,7 +1104,7 @@ void FragmentPaintPropertyTreeBuilder::UpdateOverflowControlsClip() {
   if (!NeedsPaintPropertyUpdate())
     return;
 
-  if (NeedsOverflowControlsClip(object_)) {
+  if (NeedsOverflowControlsClip()) {
     // Clip overflow controls to the border box rect.
     properties_->UpdateOverflowControlsClip(
         context_.current.clip, context_.current.transform,
@@ -2296,8 +2299,7 @@ bool ObjectPaintPropertyTreeBuilder::UpdateFragments() {
       NeedsFilter(object_) || NeedsCssClip(object_) ||
       NeedsInnerBorderRadiusClip(object_) || NeedsOverflowClip(object_) ||
       NeedsPerspective(object_) || NeedsSVGLocalToBorderBoxTransform(object_) ||
-      NeedsScrollOrScrollTranslation(object_) ||
-      NeedsOverflowControlsClip(object_);
+      NeedsScrollOrScrollTranslation(object_);
   // Need of fragmentation clip will be determined in CreateFragmentContexts().
 
   if (!NeedsFragmentation()) {

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilderTest.cpp

@@ -5113,15 +5113,7 @@ TEST_P(PaintPropertyTreeBuilderTest, OverflowControlsClipSubpixel) {
 
   const auto* properties2 = PaintPropertiesForElement("div2");
   ASSERT_NE(nullptr, properties2);
-  EXPECT_NE(nullptr, properties2->OverflowControlsClip());
-  const auto* overflow_controls_clip2 = properties2->OverflowControlsClip();
-  if (RuntimeEnabledFeatures::SlimmingPaintV175Enabled()) {
-    EXPECT_EQ(FloatRect(0, 0, 51, 50),
-              overflow_controls_clip2->ClipRect().Rect());
-  } else {
-    EXPECT_EQ(FloatRect(0, 0, 50.5, 50),
-              overflow_controls_clip2->ClipRect().Rect());
-  }
+  EXPECT_EQ(nullptr, properties2->OverflowControlsClip());
 }
 
 TEST_P(PaintPropertyTreeBuilderTest, FragmentPaintOffsetUnderOverflowScroll) {