[blink-gen-property-trees] Always add scroll node for layout view

The layout test crash because:

1. We always create scrollbar layers even the outer viewport does not scrollable
2. Outer viewport does not scrollable then we don't create scroll node in
   NeedsScrollNode.
3. cc gen property trees alway create scroll node because it is scrollable in
   cc side (RequiresCompositingForRootScroller).

In this patch, we always add scroll node for layout view. After this CL, some
tests in virtual/android/fullscreen still failure but not crash, devtools mobile
emulator still other crash.

Bug: 865560
Cq-Include-Trybots: luci.chromium.try:linux-blink-gen-property-trees;luci.chromium.try:linux_layout_tests_layout_ng;luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I21a54cf7739055832b4634e28b850bf63543d9ed
Reviewed-on: https://chromium-review.googlesource.com/1156002
Commit-Queue: Jianpeng Chao <chaopeng@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584169}

third_party/WebKit/LayoutTests/TestExpectations

@@ -4978,3 +4978,5 @@ crbug.com/869726 [ Mac ] virtual/scroll_customization/fast/events/touch/touch-la
 # Test frequently times out on Mac CQ bots.
 crbug.com/874703 [ Mac ] http/tests/devtools/extensions/extensions-panel.js [ Timeout Pass ]
 
+# This won't pass until the bug fixed.
+crbug.com/875287 fast/frames/crash-frameset-CSS-content-property.html [ Crash ]
\ No newline at end of file

third_party/blink/renderer/core/paint/compositing/compositing_reason_finder.cc

@@ -256,7 +256,11 @@ bool CompositingReasonFinder::RequiresCompositingForRootScroller(
     const PaintLayer& layer) {
   // The root scroller needs composited scrolling layers even if it doesn't
   // actually have scrolling since CC has these assumptions baked in for the
-  // viewport.
+  // viewport. Because this is only needed for CC, we can skip it if compositing
+  // is not enabled.
+  const auto& settings = *layer.GetLayoutObject().GetDocument().GetSettings();
+  if (!settings.GetAcceleratedCompositingEnabled())
+    return false;
   return RootScrollerUtil::IsGlobal(layer);
 }
 

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

@@ -98,7 +98,12 @@ TEST_P(PaintControllerPaintTest, ChunkIdClientCacheFlag) {
   // Verify that the background does not scroll.
   const PaintChunk& background_chunk = RootPaintController().PaintChunks()[0];
   auto* transform = background_chunk.properties.Transform();
-  EXPECT_EQ(nullptr, transform->ScrollNode());
+  // TODO(crbug.com/732611): SPv2 invalidations are incorrect if there is
+  // scrolling.
+  if (RuntimeEnabledFeatures::SlimmingPaintV2Enabled())
+    EXPECT_FALSE(transform->ScrollNode());
+  else
+    EXPECT_TRUE(transform->ScrollNode());
 
   const EffectPaintPropertyNode* effect_node =
       div.FirstFragment().PaintProperties()->Effect();

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

@@ -187,23 +187,39 @@ class FragmentPaintPropertyTreeBuilder {
   bool property_added_or_removed_ = false;
 };
 
+static bool IsRootScroller(const LayoutBox& box) {
+  auto* scrollable_area = box.GetScrollableArea();
+  DCHECK(scrollable_area);
+  auto* layer = scrollable_area->Layer();
+  return layer &&
+         CompositingReasonFinder::RequiresCompositingForRootScroller(*layer);
+}
+
+static bool HasScrollsOverflow(const LayoutBox& box) {
+  // TODO(crbug.com/839341): Remove ScrollTimeline check once we support
+  // main-thread AnimationWorklet and don't need to promote the scroll-source.
+  return box.GetScrollableArea()->ScrollsOverflow() ||
+         ScrollTimeline::HasActiveScrollTimeline(box.GetNode());
+}
+
 static bool NeedsScrollNode(const LayoutObject& object) {
   if (!object.HasOverflowClip())
     return false;
-  // TODO(crbug.com/839341): Remove ScrollTimeline check once we support
-  // main-thread AnimationWorklet and don't need to promote the scroll-source.
-  return ToLayoutBox(object).GetScrollableArea()->ScrollsOverflow() ||
-         ScrollTimeline::HasActiveScrollTimeline(object.GetNode());
+  const LayoutBox& box = ToLayoutBox(object);
+  // TODO(pdr): SPV2 has invalidation issues (crbug.com/732611) as well as
+  // subpixel issues (crbug.com/693741) which prevent us from compositing the
+  // root scroller.
+  if (RuntimeEnabledFeatures::SlimmingPaintV2Enabled())
+    return HasScrollsOverflow(box);
+  return HasScrollsOverflow(box) || IsRootScroller(box);
 }
 
 static CompositingReasons CompositingReasonsForScroll(const LayoutBox& box) {
   CompositingReasons compositing_reasons = CompositingReason::kNone;
-  if (auto* scrollable_area = box.GetScrollableArea()) {
-    if (auto* layer = scrollable_area->Layer()) {
-      if (CompositingReasonFinder::RequiresCompositingForRootScroller(*layer))
-        compositing_reasons |= CompositingReason::kRootScroller;
-    }
-  }
+
+  if (IsRootScroller(box))
+    compositing_reasons |= CompositingReason::kRootScroller;
+
   // TODO(pdr): Set other compositing reasons for scroll here, see:
   // PaintLayerScrollableArea::ComputeNeedsCompositedScrolling.
   return compositing_reasons;
@@ -1449,10 +1465,8 @@ void FragmentPaintPropertyTreeBuilder::UpdateScrollAndScrollTranslation() {
 
   if (properties_->Scroll())
     context_.current.scroll = properties_->Scroll();
-  if (properties_->ScrollTranslation()) {
+  if (properties_->ScrollTranslation())
     context_.current.transform = properties_->ScrollTranslation();
-    context_.current.should_flatten_inherited_transform = false;
-  }
 }
 
 void FragmentPaintPropertyTreeBuilder::UpdateOutOfFlowContext() {