[LayoutNG] Don't generate break opportunity right after forced break

A generated break opportunity right after a forced break is always
redundant, as there's already a break. So this patch stops adding it.

Bug: 976568
Change-Id: Ia0ef3f608981ba407549358889f388ddff438f8f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1668058
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Auto-Submit: Xiaocheng Hu <xiaochengh@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#671027}

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

@@ -554,7 +554,12 @@ void NGInlineItemsBuilderTemplate<
           // removed entirely. However, when the first collapsible space is
           // 'nowrap', and the following collapsed space is 'wrap', the
           // collapsed space needs to create a break opportunity.
-          AppendGeneratedBreakOpportunity(layout_object);
+          // Note that we don't need to generate a break opportunity right
+          // after a forced break.
+          if (item->Type() != NGInlineItem::kControl ||
+              text_[item->StartOffset()] != kNewlineCharacter) {
+            AppendGeneratedBreakOpportunity(layout_object);
+          }
         }
       }
     } else {

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

@@ -9,6 +9,7 @@
 #include "third_party/blink/renderer/core/dom/dom_token_list.h"
 #include "third_party/blink/renderer/core/dom/element_traversal.h"
 #include "third_party/blink/renderer/core/dom/text.h"
+#include "third_party/blink/renderer/core/html_names.h"
 #include "third_party/blink/renderer/core/layout/ng/inline/ng_inline_child_layout_context.h"
 #include "third_party/blink/renderer/core/layout/ng/inline/ng_inline_layout_algorithm.h"
 #include "third_party/blink/renderer/core/layout/ng/inline/ng_physical_line_box_fragment.h"
@@ -1520,6 +1521,24 @@ TEST_F(NGInlineNodeTest, InsertedWBRWithLineBreakInRelayout) {
   EXPECT_EQ(String(u"foo\u200Bbar"), GetText());
 }
 
+TEST_F(NGInlineNodeTest, CollapsibleSpaceFollowingBRWithNoWrapStyle) {
+  SetupHtml("t", "<div id=t><span style=white-space:pre><br></span> </div>");
+  EXPECT_EQ("\n", GetText());
+
+  GetDocument().QuerySelector("span")->removeAttribute(html_names::kStyleAttr);
+  UpdateAllLifecyclePhasesForTest();
+  EXPECT_EQ("\n", GetText());
+}
+
+TEST_F(NGInlineNodeTest, CollapsibleSpaceFollowingNewlineWithPreStyle) {
+  SetupHtml("t", "<div id=t><span style=white-space:pre>\n</span> </div>");
+  EXPECT_EQ("\n", GetText());
+
+  GetDocument().QuerySelector("span")->removeAttribute(html_names::kStyleAttr);
+  UpdateAllLifecyclePhasesForTest();
+  EXPECT_EQ("", GetText());
+}
+
 #if SEGMENT_BREAK_TRANSFORMATION_FOR_EAST_ASIAN_WIDTH
 // https://crbug.com/879088
 TEST_F(NGInlineNodeTest, RemoveSegmentBreakFromJapaneseInRelayout) {