Enable rewind-loop detector in NGLineBreaker in non-DCHECK builds

Currently the infinite rewind loop does not frequently occur,
but it exists, and recent issues indicated that minor changes
may hit it. This patch enables the rewind-loop detector added
for DCHECK-builds in r696740 crrev.com/c/1801474 for non-
DCHECK-builds. When it hits, it fires |NOTREACHED| and end the
line breaker.

This patch also fixes the detector not to misfire when
rewinding to index 0 by using |Optional|.

Bug: 1132811
Change-Id: Idc4a8de5484b8f2df90b7f8525139ae99be6b9aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2498983Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821075}

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

@@ -743,12 +743,12 @@ void NGLineBreaker::HandleText(const NGInlineItem& item,
 
     // Hanging trailing spaces may resolve the overflow.
     if (item_result->has_only_trailing_spaces) {
+      state_ = LineBreakState::kTrailing;
       if (item_result->item->Style()->WhiteSpace() == EWhiteSpace::kPreWrap &&
           IsBreakableSpace(Text()[item_result->EndOffset() - 1])) {
         unsigned end_index = item_result - line_info->Results().begin();
         Rewind(end_index, line_info);
       }
-      state_ = LineBreakState::kTrailing;
       return;
     }
 
@@ -1977,7 +1977,7 @@ void NGLineBreaker::HandleOverflow(NGLineInfo* line_info) {
 
           // If this is the last item, adjust it to accommodate the change.
           const unsigned new_end = i + 1;
-          DCHECK_LE(new_end, item_results->size());
+          CHECK_LE(new_end, item_results->size());
           if (new_end == item_results->size()) {
             position_ =
                 available_width + width_to_rewind + item_result->inline_size;
@@ -1989,11 +1989,8 @@ void NGLineBreaker::HandleOverflow(NGLineInfo* line_info) {
             return;
           }
 
-          Rewind(new_end, line_info);
-          if (new_end < item_results->size())
           state_ = LineBreakState::kTrailing;
-          else
-            HandleTrailingSpaces(item, line_info);
+          Rewind(new_end, line_info);
           return;
         }
 
@@ -2011,11 +2008,11 @@ void NGLineBreaker::HandleOverflow(NGLineInfo* line_info) {
   if (!override_break_anywhere_ && has_break_anywhere_if_overflow) {
     override_break_anywhere_ = true;
     break_iterator_.SetBreakType(LineBreakType::kBreakCharacter);
+    state_ = LineBreakState::kContinue;
     // TODO(kojii): Not all items need to rewind, but such case is rare and
     // rewinding all items simplifes the code.
     if (!item_results->IsEmpty())
       Rewind(0, line_info);
-    state_ = LineBreakState::kContinue;
     ResetRewindLoopDetector();
     return;
   }
@@ -2078,11 +2075,12 @@ void NGLineBreaker::RewindOverflow(unsigned new_end, NGLineInfo* line_info) {
           }
           // If this item starts with spaces followed by non-space characters,
           // the line should break after the spaces. Rewind to before this item.
-          Rewind(index, line_info);
-          // Now we want to |HandleTrailingSpaces| in this |item|, but |Rewind|
-          // may have failed when we have floats. Set the |state_| to
-          // |kTrailing| and let the next |HandleText| to handle this.
+          //
+          // After the rewind, we want to |HandleTrailingSpaces| in this |item|,
+          // but |Rewind| may have failed when we have floats. Set the |state_|
+          // to |kTrailing| and let the next |HandleText| to handle this.
           state_ = LineBreakState::kTrailing;
+          Rewind(index, line_info);
           return;
         }
       }
@@ -2145,18 +2143,19 @@ void NGLineBreaker::RewindOverflow(unsigned new_end, NGLineInfo* line_info) {
 }
 
 void NGLineBreaker::Rewind(unsigned new_end, NGLineInfo* line_info) {
-#if DCHECK_IS_ON()
-  // Detect rewind-loop. If we're trying to rewind to the same index twice,
-  // we're in the infinite loop.
-  DCHECK(item_index_ != last_rewind_from_item_index_ ||
-         new_end != last_rewind_to_item_index_)
-      << item_index_ << ", " << offset_ << "->" << new_end;
-  last_rewind_from_item_index_ = item_index_;
-  last_rewind_to_item_index_ = new_end;
-#endif
-
   NGInlineItemResults& item_results = *line_info->MutableResults();
   DCHECK_LT(new_end, item_results.size());
+  if (last_rewind_) {
+    // Detect rewind-loop. If we're trying to rewind to the same index twice,
+    // we're in the infinite loop.
+    if (item_index_ == last_rewind_->from_item_index &&
+        new_end == last_rewind_->to_index) {
+      NOTREACHED();
+      state_ = LineBreakState::kDone;
+      return;
+    }
+    last_rewind_.emplace(RewindIndex{item_index_, new_end});
+  }
 
   // Avoid rewinding floats if possible. They will be added back anyway while
   // processing trailing items even when zero available width. Also this saves

third_party/blink/renderer/core/layout/ng/inline/ng_line_breaker.h

@@ -183,11 +183,7 @@ class CORE_EXPORT NGLineBreaker {
   void HandleOverflow(NGLineInfo*);
   void RewindOverflow(unsigned new_end, NGLineInfo*);
   void Rewind(unsigned new_end, NGLineInfo*);
-  void ResetRewindLoopDetector() {
-#if DCHECK_IS_ON()
-    last_rewind_from_item_index_ = last_rewind_to_item_index_ = 0;
-#endif
-  }
+  void ResetRewindLoopDetector() { last_rewind_.reset(); }
 
   const ComputedStyle& ComputeCurrentStyle(unsigned item_result_index,
                                            NGLineInfo*) const;
@@ -338,11 +334,12 @@ class CORE_EXPORT NGLineBreaker {
   LayoutUnit cloned_box_decorations_end_size_;
   bool has_cloned_box_decorations_ = false;
 
-#if DCHECK_IS_ON()
   // These fields are to detect rewind-loop.
-  unsigned last_rewind_from_item_index_ = 0;
-  unsigned last_rewind_to_item_index_ = 0;
-#endif
+  struct RewindIndex {
+    wtf_size_t from_item_index;
+    wtf_size_t to_index;
+  };
+  base::Optional<RewindIndex> last_rewind_;
 };
 
 }  // namespace blink