[balance-text] Fix divide-by-zero when very narrow

This patch fixes divide-by-zero error in `EstimateNumLines` when the available width is smaller than `1ch`. Bug: 1251079 Change-Id: I15888e6e8bbd0a0efb9dad5229dbef1050d668f9 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4295483 Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org> Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org> Auto-Submit: Koji Ishii <kojii@chromium.org> Cr-Commit-Position: refs/heads/main@{#1111030}
qweri0p · Feb 28, 2023 · 3bd809f · 3bd809f
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diff --git a/third_party/blink/renderer/core/layout/ng/inline/ng_paragraph_line_breaker.cc b/third_party/blink/renderer/core/layout/ng/inline/ng_paragraph_line_breaker.cc
@@ -106,7 +106,15 @@ wtf_size_t EstimateNumLines(const String& text_content,
                             const SimpleFontData* font,
                             LayoutUnit available_width) {
   const float space_width = font->SpaceWidth();
+  if (space_width <= 0) {
+    // Can't estimate without space glyph, go on to measure the actual value.
+    return 0;
+  }
   const wtf_size_t num_line_chars = available_width / space_width;
+  if (num_line_chars <= 0) {
+    // The width is too narrow, don't balance.
+    return std::numeric_limits<wtf_size_t>::max();
+  }
   return (text_content.length() + num_line_chars - 1) / num_line_chars;
 }
 

diff --git a/...blink/web_tests/external/wpt/css/css-text/white-space/text-wrap-balance-narrow-crash.html b/...blink/web_tests/external/wpt/css/css-text/white-space/text-wrap-balance-narrow-crash.html
@@ -0,0 +1,2 @@
+<!DOCTYPE html>
+<div style="width: 1px; text-wrap: balance">A</div>
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		<!DOCTYPE html>
		<div style="width: 1px; text-wrap: balance">A</div>