[LayoutNG] Add scrolled offset when hit testing scrolled content

This patch takes scrolled offset into account when hit testing the
children of a scroll container, so that scrolled contents can be hit
tested correctly.

Bug: 855279
Cq-Include-Trybots: 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: Ic84b40c06302c457cf32cacaa5e79f419dcc3a2b
Reviewed-on: https://chromium-review.googlesource.com/1125312Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572398}

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

@@ -418,7 +418,6 @@ crbug.com/591099 fast/dynamic/first-letter-after-list-marker.html [ Failure ]
 crbug.com/591099 fast/dynamic/text-combine.html [ Failure ]
 crbug.com/591099 fast/encoding/utf-16-big-endian.html [ Failure ]
 crbug.com/591099 fast/encoding/utf-16-little-endian.html [ Failure ]
-crbug.com/591099 fast/events/mouse-relative-position.html [ Failure ]
 crbug.com/591099 fast/events/select-element.html [ Failure ]
 crbug.com/591099 fast/events/touch/compositor-touch-hit-rects.html [ Failure ]
 crbug.com/591099 fast/events/wheel/mainthread-touchpad-fling-latching.html [ Pass ]
@@ -716,7 +715,6 @@ crbug.com/591099 paint/invalidation/svg/resize-svg-invalidate-children-2.html [
 crbug.com/714962 paint/invalidation/svg/resize-svg-invalidate-children-fixed-size-relative-child.html [ Failure ]
 crbug.com/591099 paint/invalidation/svg/resize-svg-invalidate-children.html [ Failure ]
 crbug.com/591099 paint/invalidation/svg/scale-change-huge-geometry.html [ Failure ]
-crbug.com/591099 paint/invalidation/svg/scroll-hit-test.xhtml [ Failure ]
 crbug.com/728378 paint/invalidation/svg/scrolling-embedded-svg-file-image-repaint-problem.html [ Failure ]
 # rightsizing-grid.html is truly flaky, show flakiness on reload
 crbug.com/591099 svg/wicd/rightsizing-grid.html [ Pass Failure ]
@@ -799,7 +797,6 @@ crbug.com/591099 virtual/gpu/fast/canvas/shadow-huge-blur.html [ Pass ]
 crbug.com/591099 virtual/layout_ng/ [ Skip ]
 crbug.com/824918 virtual/layout_ng_experimental/ [ Skip ]
 crbug.com/591099 virtual/mojo-blob-urls/external/wpt/FileAPI/url/sandboxed-iframe.html [ Pass ]
-crbug.com/591099 virtual/mouseevent_fractional/fast/events/mouse-relative-position.html [ Failure ]
 crbug.com/591099 virtual/mouseevent_fractional/fast/events/select-element.html [ Failure ]
 crbug.com/591099 virtual/mouseevent_fractional/fast/events/touch/compositor-touch-hit-rects.html [ Failure ]
 crbug.com/591099 virtual/mouseevent_fractional/fast/events/wheel/mainthread-touchpad-fling-latching.html [ Pass ]
@@ -819,7 +816,6 @@ crbug.com/591099 virtual/stable/ [ Skip ]
 crbug.com/591099 virtual/threaded/ [ Skip ]
 crbug.com/591099 virtual/user-activation-v2/fast/dom/Window/window-lookup-precedence.html [ Failure ]
 crbug.com/591099 virtual/user-activation-v2/fast/events/mouse-cursor.html [ Failure ]
-crbug.com/591099 virtual/user-activation-v2/fast/events/mouse-relative-position.html [ Failure ]
 crbug.com/591099 virtual/user-activation-v2/fast/events/select-element.html [ Failure ]
 crbug.com/591099 virtual/user-activation-v2/fast/events/touch/compositor-touch-hit-rects.html [ Failure ]
 crbug.com/591099 virtual/user-activation-v2/fullscreen/full-screen-with-flex-item.html [ Failure ]

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

@@ -876,10 +876,15 @@ bool NGBoxFragmentPainter::NodeAtPoint(
     }
   }
 
-  if (!skip_children &&
-      HitTestChildren(result, box_fragment_.Children(), location_in_container,
-                      physical_offset, action)) {
-    return true;
+  if (!skip_children) {
+    const IntSize scrolled_offset =
+        box_fragment_.HasOverflowClip()
+            ? PhysicalFragment().ScrolledContentOffset()
+            : IntSize();
+    if (HitTestChildren(result, box_fragment_.Children(), location_in_container,
+                        physical_offset - scrolled_offset, action)) {
+      return true;
+    }
   }
 
   if (style.HasBorderRadius() &&

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

@@ -114,8 +114,9 @@ class NGBoxFragmentPainter : public BoxPainterBase {
 
   // Hit tests the children of a container fragment, which is either
   // |box_fragment_|, or one of its child line box fragments.
-  // @param physical_offset Physical offset of the container fragment in paint
-  // layer.
+  // @param physical_offset Physical offset of the container fragment's content
+  // box in paint layer. Note that this includes scrolling offset when the
+  // container has 'overflow: scroll'.
   bool HitTestChildren(HitTestResult&,
                        const Vector<std::unique_ptr<NGPaintFragment>>&,
                        const HitTestLocation& location_in_container,