Fix hit testing culled inline when text is fragmented

This patch fixes hit testing culled inline when a text node
(or LayoutText) is fragmented. This can happen for trailing
spaces, `::first-letter`, and a few other cases.

|HitTestCulledInlineAncestors| checks if the current fragment
is the first one in the line, but only by checking
|LayoutObject|, so it fails when a |LayoutObject| is
fragmented. This patch adds check if the current fragment is
from the same |LayoutObject| as the previous sibling.

Bug: 1009042
Change-Id: Id9cd8b834528bda999fb557e0a6f0d2aeec69e4e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2262401Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781846}

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

@@ -280,6 +280,34 @@ TEST_P(ParameterizedLayoutInlineTest, MultilineRelativePositionedHitTest) {
   }
 }
 
+TEST_P(ParameterizedLayoutInlineTest, HitTestCulledInlinePreWrap) {
+  SetBodyInnerHTML(R"HTML(
+    <style>
+      html, body { margin: 0; }
+      body {
+        width: 250px;
+      }
+      span {
+        white-space: pre-wrap;
+        font: 30px serif;
+      }
+    </style>
+    <div id="container">
+      <span id="span">The quick brown fox jumps over the lazy dog.</span>
+    </div>
+  )HTML");
+  HitTestRequest hit_request(HitTestRequest::kReadOnly);
+  PhysicalOffset hit_location(100, 15);
+  HitTestLocation location(hit_location);
+  HitTestResult hit_result(hit_request, location);
+  LayoutObject* container = GetLayoutObjectByElementId("container");
+  container->HitTestAllPhases(hit_result, location, PhysicalOffset());
+
+  Element* span = GetElementById("span");
+  Node* text_node = span->firstChild();
+  EXPECT_EQ(hit_result.InnerNode(), text_node);
+}
+
 TEST_P(ParameterizedLayoutInlineTest, VisualRectInDocument) {
   LoadAhem();
   SetBodyInnerHTML(R"HTML(

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

@@ -125,6 +125,11 @@ bool HitTestCulledInlineAncestors(
     const HitTestLocation& hit_test_location,
     const PhysicalOffset fallback_accumulated_offset) {
   DCHECK(current != limit && current->IsDescendantOf(limit));
+
+  // Check ancestors only when |current| is the first fragment in this line.
+  if (previous_sibling && current == previous_sibling.GetLayoutObject())
+    return false;
+
   for (LayoutObject* parent = current->Parent(); parent && parent != limit;
        current = parent, parent = parent->Parent()) {
     // |culled_parent| is a culled inline element to be hit tested, since it's