[LayoutNG] Ignore scrollbars in anonymous constraint spaces.

We already did ignore borders and padding, but forgot about scrollbars. This was quite catastrophic for multicol, if a horizontal scrollbar was actually taller than the columns. We'd end up pushing the scrollbar in front of us (in block direction), column after column. Infinite loop (until OOM). Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng Change-Id: I5c3038406ccf30eeb0e107b31c6bb783c7089ffd Reviewed-on: https://chromium-review.googlesource.com/702299Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org> Commit-Queue: Morten Stenshorne <mstensho@opera.com> Cr-Commit-Position: refs/heads/master@{#506844}

[LayoutNG] Ignore scrollbars in anonymous constraint spaces.
We already did ignore borders and padding, but forgot about scrollbars. This was quite catastrophic for multicol, if a horizontal scrollbar was actually taller than the columns. We'd end up pushing the scrollbar in front of us (in block direction), column after column. Infinite loop (until OOM). Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng Change-Id: I5c3038406ccf30eeb0e107b31c6bb783c7089ffd Reviewed-on: https://chromium-review.googlesource.com/702299Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org> Commit-Queue: Morten Stenshorne <mstensho@opera.com> Cr-Commit-Position: refs/heads/master@{#506844}
4fb8e7be · Morten Stenshorne · Commit Bot · 2d9d8fa7 · 4fb8e7be · 4fb8e7be
Commit 4fb8e7be authored Oct 05, 2017 by Morten Stenshorne Committed by Commit Bot Oct 05, 2017
2 changed files
--- a/third_party/WebKit/LayoutTests/fast/multicol/scrollbar-taller-than-content-box-freeze.html
+++ b/third_party/WebKit/LayoutTests/fast/multicol/scrollbar-taller-than-content-box-freeze.html
+<!DOCTYPE html>
+<div style="overflow:scroll; columns:2; column-fill:auto; height:1px;">
+     <div style="height:2px;"></div>
+</div>
+<script src="../../resources/testharness.js"></script>
+<script src="../../resources/testharnessreport.js"></script>
+<script>
+    test(() => { }, "PASS if no freeze, crash or assertion failure");
+</script>
--- a/third_party/WebKit/Source/core/layout/ng/ng_length_utils.cc
+++ b/third_party/WebKit/Source/core/layout/ng/ng_length_utils.cc
@@ -534,6 +534,11 @@ NGBoxStrut CalculateBorderScrollbarPadding(
    const NGConstraintSpace& constraint_space,
    const ComputedStyle& style,
    const NGBlockNode node) {
+  // If we are producing an anonymous fragment (e.g. a column), it has no
+  // borders, padding or scrollbars. Using the ones from the container can only
+  // cause trouble.
+  if (constraint_space.IsAnonymous())
+    return NGBoxStrut();
  return ComputeBorders(constraint_space, style) +
         ComputePadding(constraint_space, style) + node.GetScrollbarSizes();
 }