[LayoutNG] Apply segment break transformation rules before reusing inline items

When a text node starts with a space run that contains newlines, it's
possible that the text node's inline items can't be reused in relayout
due to segment break transformation rules.

This patch applies the rules to check if the newline is handled
differently in relayout, and if so, stops reusing the old inline items.

Bug: 969089
Change-Id: I163b2542154ea79971fb13922489441873c1712b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1641989Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#665689}

third_party/blink/renderer/core/layout/ng/inline/ng_inline_items_builder.cc

@@ -315,12 +315,26 @@ bool NGInlineItemsBuilderTemplate<OffsetMappingBuilder>::AppendTextReusing(
           }
           break;
         case NGInlineItem::kNotCollapsible: {
-          // If the start of the original string was collapsed, it may be
-          // restored.
           const String& source_text = layout_text->GetText();
-          if (source_text.length() && IsCollapsibleSpace(source_text[0]) &&
-              original_string[old_item0.StartOffset()] != kSpaceCharacter)
-            return false;
+          if (source_text.length() && IsCollapsibleSpace(source_text[0])) {
+            // If the start of the original string was collapsed, it may be
+            // restored.
+            if (original_string[old_item0.StartOffset()] != kSpaceCharacter)
+              return false;
+            // If the start of the original string was not collapsed, and the
+            // collapsible space run contains newline, the newline may be
+            // removed.
+            unsigned offset = 0;
+            UChar c = source_text[0];
+            bool contains_newline =
+                MoveToEndOfCollapsibleSpaces(source_text, &offset, &c);
+            if (contains_newline &&
+                ShouldRemoveNewline(text_, text_.length(), last_item->Style(),
+                                    StringView(source_text, offset),
+                                    &new_style)) {
+              return false;
+            }
+          }
           break;
         }
         case NGInlineItem::kCollapsed:

third_party/blink/renderer/core/layout/ng/inline/ng_inline_node_test.cc

@@ -1432,6 +1432,20 @@ TEST_F(NGInlineNodeTest, PreservedNewlineWithRemovedBidiAndRelayout) {
   EXPECT_EQ("foo\nbar", GetText());
 }
 
+// https://crbug.com/969089
+TEST_F(NGInlineNodeTest, InsertedWBRWithLineBreakInRelayout) {
+  SetupHtml("container", "<div id=container><span>foo</span>\nbar</div>");
+  EXPECT_EQ("foo bar", GetText());
+
+  Element* div = GetElementById("container");
+  Element* wbr = GetDocument().CreateElementForBinding("wbr");
+  div->insertBefore(wbr, div->lastChild());
+  UpdateAllLifecyclePhasesForTest();
+
+  // The '\n' should be collapsed by the inserted <wbr>
+  EXPECT_EQ(String(u"foo\u200Bbar"), GetText());
+}
+
 #if SEGMENT_BREAK_TRANSFORMATION_FOR_EAST_ASIAN_WIDTH
 // https://crbug.com/879088
 TEST_F(NGInlineNodeTest, RemoveSegmentBreakFromJapaneseInRelayout) {