Temporarily disable composited scrolling optimization for css-clip/clip-path

This is to evaluate the performance improvement of the optimization in
1 or 2 canary builds. Will revert after that.

This disables the optimization for composited scrolling added in
crrev.com/774232.

Bug 1113269

Change-Id: I2cf85fd5e550c1fef7d29f76b90e5d1b7219d579
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2353066
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797532}

third_party/blink/renderer/core/layout/layout_box_model_object.cc

@@ -126,6 +126,11 @@ LayoutBoxModelObject::ComputeBackgroundPaintLocationIfComposited() const {
       return kBackgroundPaintInScrollingContents;
   }
 
+  // TODO(crbug.com/1113269): Temporarily disable composited scrolling for
+  // clipped layers.
+  if (HasClip())
+    return kBackgroundPaintInGraphicsLayer;
+
   // Inset box shadow is painted in the scrolling area above the background, and
   // it doesn't scroll, so the background can only be painted in the main layer.
   if (HasInsetBoxShadow(StyleRef()))

third_party/blink/renderer/core/page/scrolling/main_thread_scrolling_reasons_test.cc

@@ -397,10 +397,13 @@ TEST_F(NonCompositedMainThreadScrollingReasonsTest,
       cc::MainThreadScrollingReason::kCantPaintScrollingBackgroundAndLCDText);
 }
 
+#if 0
+// TODO(crbug.com/1113269): Temporarily disabled.
 TEST_F(NonCompositedMainThreadScrollingReasonsTest, ClipTest) {
   TestNonCompositedReasons("clip",
                            cc::MainThreadScrollingReason::kNotScrollingOnMain);
 }
+#endif
 
 TEST_F(NonCompositedMainThreadScrollingReasonsTest, ClipPathTest) {
   TestNonCompositedReasons(

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

@@ -165,6 +165,7 @@ PaintLayer::PaintLayer(LayoutBoxModelObject& layout_object)
       previous_paint_result_(kFullyPainted),
       needs_paint_phase_descendant_outlines_(false),
       needs_paint_phase_float_(false),
+      has_descendant_with_clip_path_(false),
       has_non_isolated_descendant_with_blend_mode_(false),
       has_fixed_position_descendant_(false),
       has_sticky_position_descendant_(false),
@@ -611,6 +612,7 @@ void PaintLayer::UpdateDescendantDependentFlags() {
         has_non_isolated_descendant_with_blend_mode_;
     has_visible_descendant_ = false;
     has_non_isolated_descendant_with_blend_mode_ = false;
+    has_descendant_with_clip_path_ = false;
     has_fixed_position_descendant_ = false;
     has_sticky_position_descendant_ = false;
     has_non_contained_absolute_position_descendant_ = false;
@@ -644,6 +646,9 @@ void PaintLayer::UpdateDescendantDependentFlags() {
            child->HasNonIsolatedDescendantWithBlendMode()) ||
           child_style.HasBlendMode();
 
+      has_descendant_with_clip_path_ |= child->HasDescendantWithClipPath() ||
+                                        child->GetLayoutObject().HasClipPath();
+
       has_fixed_position_descendant_ |=
           child->HasFixedPositionDescendant() ||
           child_style.GetPosition() == EPosition::kFixed;

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

@@ -895,6 +895,11 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
   const PaintLayer* MaskAncestor() const {
     return GetAncestorDependentCompositingInputs().mask_ancestor;
   }
+  // TODO(crbug.com/1113269): Temporary.
+  bool HasDescendantWithClipPath() const {
+    DCHECK(!needs_descendant_dependent_flags_update_);
+    return has_descendant_with_clip_path_;
+  }
   bool HasFixedPositionDescendant() const {
     DCHECK(!needs_descendant_dependent_flags_update_);
     return has_fixed_position_descendant_;
@@ -1348,6 +1353,9 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
   unsigned needs_paint_phase_descendant_outlines_ : 1;
   unsigned needs_paint_phase_float_ : 1;
 
+  // TODO(crbug.com/1113269): Temporary.
+  unsigned has_descendant_with_clip_path_ : 1;
+
   // These bitfields are part of ancestor/descendant dependent compositing
   // inputs.
   unsigned has_non_isolated_descendant_with_blend_mode_ : 1;

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

@@ -2616,6 +2616,15 @@ bool PaintLayerScrollableArea::ComputeNeedsCompositedScrollingInternal(
     }
   }
 
+  // TODO(crbug.com/1113269): Temporary.
+  if (box->HasClip() || layer_->HasDescendantWithClipPath() ||
+      !!layer_->ClipPathAncestor()) {
+    non_composited_main_thread_scrolling_reasons_ |=
+        // Just a random flag to disable composited scrolling.
+        cc::MainThreadScrollingReason::kCantPaintScrollingBackgroundAndLCDText;
+    needs_composited_scrolling = false;
+  }
+
   DCHECK(!(non_composited_main_thread_scrolling_reasons_ &
            ~cc::MainThreadScrollingReason::kNonCompositedReasons));
   return needs_composited_scrolling;

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

@@ -319,7 +319,8 @@ TEST_P(PaintLayerScrollableAreaTest,
             GetBackgroundPaintLocation("scroller15"));
 
   // css-clip doesn't affect background paint location.
-  EXPECT_EQ(kBackgroundPaintInScrollingContents,
+  // TODO(crbug.com/1113269): Temporary.
+  EXPECT_EQ(kBackgroundPaintInGraphicsLayer,
             GetBackgroundPaintLocation("css-clip"));
 
   // #scroller17 can only be painted once as it is translucent, and it must