[LayoutNG] Fix offset accumulation for hit test fallback

Current LayoutNG hit test code computes wrong |accumulated_offset|
when falling back to legacy. It tries to maintain an additional
offset for legacy, but fails to do so.

This patch computes the fallback offset directly from NG offset, which
fixes legacy fallback, and also removes the legacy offset maintenance
code.

Bug: 811502
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_layout_ng;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I06b2df66dc2a36efaf32077ea26a3abb4a26eb49
Reviewed-on: https://chromium-review.googlesource.com/1089800Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565070}

third_party/WebKit/LayoutTests/FlagExpectations/enable-blink-features=LayoutNG

@@ -1004,7 +1004,6 @@ crbug.com/591099 svg/custom/inline-svg-use-available-width-in-stf.html [ Failure
 crbug.com/591099 svg/custom/object-sizing-no-width-height.xhtml [ Failure ]
 crbug.com/591099 svg/custom/stf-container-with-intrinsic-ratio-svg.html [ Failure ]
 crbug.com/591099 svg/custom/text-match-highlight.html [ Failure ]
-crbug.com/591099 svg/custom/use-event-retargeting.html [ Failure ]
 crbug.com/591099 svg/filters/feTurbulence-bad-seeds.html [ Failure ]
 crbug.com/591099 svg/in-html/sizing/svg-inline.html [ Failure ]
 crbug.com/714962 svg/text/tspan-multiple-outline.svg [ Failure ]

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

@@ -908,7 +908,7 @@ bool LayoutInline::NodeAtPoint(HitTestResult& result,
           fragment->Parent()->InlineOffsetToContainerBox().ToLayoutPoint();
       if (NGBoxFragmentPainter(*fragment).NodeAtPoint(
               result, location_in_container, adjusted_location,
-              accumulated_offset, hit_test_action))
+              hit_test_action))
         return true;
     }
     return false;

third_party/blink/renderer/core/layout/ng/layout_ng_mixin.cc

@@ -312,7 +312,6 @@ bool LayoutNGMixin<Base>::NodeAtPoint(
     return true;
 
   return NGBlockFlowPainter(*this).NodeAtPoint(result, location_in_container,
-                                               accumulated_offset,
                                                accumulated_offset, action);
 }
 

third_party/blink/renderer/core/paint/ng/ng_block_flow_painter.cc

@@ -29,12 +29,10 @@ bool NGBlockFlowPainter::NodeAtPoint(
     HitTestResult& result,
     const HitTestLocation& location_in_container,
     const LayoutPoint& accumulated_offset,
-    const LayoutPoint& accumulated_offset_for_legacy,
     HitTestAction action) {
   if (const NGPaintFragment* paint_fragment = block_.PaintFragment()) {
     return NGBoxFragmentPainter(*paint_fragment)
-        .NodeAtPoint(result, location_in_container, accumulated_offset,
-                     accumulated_offset_for_legacy, action);
+        .NodeAtPoint(result, location_in_container, accumulated_offset, action);
   }
   return false;
 }

third_party/blink/renderer/core/paint/ng/ng_block_flow_painter.h

@@ -32,7 +32,6 @@ class NGBlockFlowPainter {
   bool NodeAtPoint(HitTestResult&,
                    const HitTestLocation& location_in_container,
                    const LayoutPoint& accumulated_offset,
-                   const LayoutPoint& accumulated_offset_for_legacy,
                    HitTestAction);
 
  private:

third_party/blink/renderer/core/paint/ng/ng_box_fragment_painter.cc

@@ -55,6 +55,25 @@ bool ShouldPaintBoxFragmentBorders(const LayoutObject& object) {
   return !ToLayoutTableCell(object).Table()->ShouldCollapseBorders();
 }
 
+// In hit testing, legacy and NG assumes different semantics for the
+// |accumulated_offset| parameter:
+// - Legacy: offset of the containing block of |child| (excluding |child| when
+// it is block by itslef) in the paint layer.
+// - NG: offset of the parent fragment in the paint layer
+// This function converts the NG offset to legacy so that hit testing can fall
+// back to legacy with the correct |accumulated_offset|.
+LayoutPoint FallbackAccumulatedOffset(const NGPaintFragment& child,
+                                      const LayoutPoint& accumulated_offset) {
+  DCHECK(child.Parent());
+  const NGPaintFragment& parent = *child.Parent();
+  if (parent.PhysicalFragment().IsBlockFlow())
+    return accumulated_offset;
+  LayoutPoint parent_inline_offset =
+      parent.InlineOffsetToContainerBox().ToLayoutPoint();
+  return accumulated_offset -
+         LayoutSize(parent_inline_offset.X(), parent_inline_offset.Y());
+}
+
 }  // anonymous namespace
 
 NGBoxFragmentPainter::NGBoxFragmentPainter(const NGPaintFragment& box)
@@ -817,7 +836,6 @@ bool NGBoxFragmentPainter::NodeAtPoint(
     HitTestResult& result,
     const HitTestLocation& location_in_container,
     const LayoutPoint& accumulated_offset,
-    const LayoutPoint& accumulated_offset_for_legacy,
     HitTestAction action) {
   // TODO(eae): Switch to using NG geometry types.
   LayoutSize offset;
@@ -859,13 +877,9 @@ bool NGBoxFragmentPainter::NodeAtPoint(
     }
   }
 
-  // TODO(layout-dev): Accumulate |accumulated_offset_for_legacy| properly.
-  LayoutPoint adjusted_location_for_legacy =
-      accumulated_offset_for_legacy + offset;
   if (!skip_children &&
       HitTestChildren(result, box_fragment_.Children(), location_in_container,
-                      adjusted_location, adjusted_location_for_legacy,
-                      action)) {
+                      adjusted_location, action)) {
     return true;
   }
 
@@ -950,7 +964,6 @@ bool NGBoxFragmentPainter::HitTestChildren(
     const Vector<std::unique_ptr<NGPaintFragment>>& children,
     const HitTestLocation& location_in_container,
     const LayoutPoint& accumulated_offset,
-    const LayoutPoint& accumulated_offset_for_legacy,
     HitTestAction action) {
   for (auto iter = children.rbegin(); iter != children.rend(); iter++) {
     const std::unique_ptr<NGPaintFragment>& child = *iter;
@@ -961,25 +974,22 @@ bool NGBoxFragmentPainter::HitTestChildren(
     bool stop_hit_testing = false;
     if (fragment.Type() == NGPhysicalFragment::kFragmentBox) {
       if (FragmentRequiresLegacyFallback(fragment)) {
+        LayoutPoint fallback_accumulated_offset =
+            FallbackAccumulatedOffset(*child, accumulated_offset);
         stop_hit_testing = fragment.GetLayoutObject()->NodeAtPoint(
-            result, location_in_container, accumulated_offset_for_legacy,
-            action);
+            result, location_in_container, fallback_accumulated_offset, action);
       } else {
-        // TODO(layout-dev): Accumulate |accumulated_offset_for_legacy|
-        // properly.
         stop_hit_testing = NGBoxFragmentPainter(*child).NodeAtPoint(
-            result, location_in_container, accumulated_offset,
-            accumulated_offset_for_legacy, action);
+            result, location_in_container, accumulated_offset, action);
       }
 
     } else if (fragment.Type() == NGPhysicalFragment::kFragmentLineBox) {
       const LayoutSize line_box_offset(fragment.Offset().left,
                                        fragment.Offset().top);
       const LayoutPoint adjusted_offset = accumulated_offset + line_box_offset;
-      // TODO(layout-dev): Accumulate |accumulated_offset_for_legacy| properly.
-      stop_hit_testing = HitTestChildren(result, child->Children(),
-                                         location_in_container, adjusted_offset,
-                                         accumulated_offset_for_legacy, action);
+      stop_hit_testing =
+          HitTestChildren(result, child->Children(), location_in_container,
+                          adjusted_offset, action);
 
     } else if (fragment.Type() == NGPhysicalFragment::kFragmentText) {
       // TODO(eae): Should this hit test on the text itself or the containing

third_party/blink/renderer/core/paint/ng/ng_box_fragment_painter.h

@@ -40,7 +40,6 @@ class NGBoxFragmentPainter : public BoxPainterBase {
   bool NodeAtPoint(HitTestResult&,
                    const HitTestLocation& location_in_container,
                    const LayoutPoint& accumulated_offset,
-                   const LayoutPoint& accumulated_offset_for_legacy,
                    HitTestAction);
 
  protected:
@@ -118,7 +117,6 @@ class NGBoxFragmentPainter : public BoxPainterBase {
                        const Vector<std::unique_ptr<NGPaintFragment>>&,
                        const HitTestLocation& location_in_container,
                        const LayoutPoint& accumulated_offset,
-                       const LayoutPoint& accumulated_offset_for_legacy,
                        HitTestAction);
   bool HitTestTextFragment(HitTestResult&,
                            const NGPaintFragment&,