[css-flexbox] More refactor: Store lines in the FlexibleBoxAlgorithm

R=eae@chromium.org

Change-Id: Ib267b515d4620ffa31de2ade2cdd4739c99027b9
Reviewed-on: https://chromium-review.googlesource.com/578391
Commit-Queue: Christian Biesinger <cbiesinger@chromium.org>
Commit-Queue: Emil A Eklund <eae@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488091}

third_party/WebKit/Source/core/layout/FlexibleBoxAlgorithm.cpp

@@ -53,35 +53,40 @@ FlexLayoutAlgorithm::FlexLayoutAlgorithm(const ComputedStyle* style,
                                          const Vector<FlexItem>& all_items)
     : style_(style),
       line_break_length_(line_break_length),
-      all_items_(all_items) {}
+      all_items_(all_items),
+      next_item_index_(0) {}
 
-bool FlexLayoutAlgorithm::ComputeNextFlexLine(size_t* next_index,
-                                              FlexLine* line) {
-  line->Reset();
+FlexLine* FlexLayoutAlgorithm::ComputeNextFlexLine() {
+  FlexLine new_line;
 
   bool line_has_in_flow_item = false;
 
-  for (; *next_index < all_items_.size(); ++*next_index) {
-    const FlexItem& flex_item = all_items_[*next_index];
+  for (; next_item_index_ < all_items_.size(); ++next_item_index_) {
+    const FlexItem& flex_item = all_items_[next_item_index_];
     DCHECK(!flex_item.box->IsOutOfFlowPositioned());
     if (IsMultiline() &&
-        line->sum_hypothetical_main_size +
+        new_line.sum_hypothetical_main_size +
                 flex_item.HypotheticalMainAxisMarginBoxSize() >
             line_break_length_ &&
         line_has_in_flow_item)
       break;
-    line->line_items.push_back(flex_item);
+    new_line.line_items.push_back(flex_item);
     line_has_in_flow_item = true;
-    line->sum_flex_base_size += flex_item.FlexBaseMarginBoxSize();
-    line->total_flex_grow += flex_item.box->Style()->FlexGrow();
-    line->total_flex_shrink += flex_item.box->Style()->FlexShrink();
-    line->total_weighted_flex_shrink +=
+    new_line.sum_flex_base_size += flex_item.FlexBaseMarginBoxSize();
+    new_line.total_flex_grow += flex_item.box->Style()->FlexGrow();
+    new_line.total_flex_shrink += flex_item.box->Style()->FlexShrink();
+    new_line.total_weighted_flex_shrink +=
         flex_item.box->Style()->FlexShrink() * flex_item.flex_base_content_size;
-    line->sum_hypothetical_main_size +=
+    new_line.sum_hypothetical_main_size +=
         flex_item.HypotheticalMainAxisMarginBoxSize();
   }
-  DCHECK(line->line_items.size() > 0 || *next_index == all_items_.size());
-  return line->line_items.size() > 0;
+  DCHECK(new_line.line_items.size() > 0 ||
+         next_item_index_ == all_items_.size());
+  if (new_line.line_items.size() > 0) {
+    flex_lines_.push_back(std::move(new_line));
+    return &flex_lines_.back();
+  }
+  return nullptr;
 }
 
 }  // namespace blink

third_party/WebKit/Source/core/layout/FlexibleBoxAlgorithm.h

@@ -75,12 +75,8 @@ class FlexItem {
 };
 
 struct FlexLine {
-  void Reset() {
-    line_items.clear();
-    sum_flex_base_size = LayoutUnit();
+  FlexLine() {
     total_flex_grow = total_flex_shrink = total_weighted_flex_shrink = 0;
-    sum_hypothetical_main_size = LayoutUnit();
-    cross_axis_offset = cross_axis_extent = max_ascent = LayoutUnit();
   }
 
   // These fields get filled in by ComputeNextFlexLine.
@@ -108,7 +104,11 @@ class FlexLayoutAlgorithm {
                       LayoutUnit line_break_length,
                       const Vector<FlexItem>& all_items);
 
-  bool ComputeNextFlexLine(size_t* next_index, FlexLine*);
+  Vector<FlexLine>& FlexLines() { return flex_lines_; }
+
+  // Computes the next flex line, stores it in FlexLines(), and returns a
+  // pointer to it. Returns nullptr if there are no more lines.
+  FlexLine* ComputeNextFlexLine();
 
  private:
   bool IsMultiline() const { return style_->FlexWrap() != EFlexWrap::kNowrap; }
@@ -116,6 +116,8 @@ class FlexLayoutAlgorithm {
   const ComputedStyle* style_;
   LayoutUnit line_break_length_;
   const Vector<FlexItem>& all_items_;
+  Vector<FlexLine> flex_lines_;
+  size_t next_item_index_;
 };
 
 }  // namespace blink

third_party/WebKit/Source/core/layout/LayoutFlexibleBox.h

@@ -198,10 +198,10 @@ class CORE_EXPORT LayoutFlexibleBox : public LayoutBlock {
   FlexItem ConstructFlexItem(LayoutBox& child, ChildLayoutType);
 
   void FreezeInflexibleItems(FlexSign,
-                             FlexLine&,
+                             FlexLine*,
                              LayoutUnit& remaining_free_space);
   bool ResolveFlexibleLengths(FlexSign,
-                              FlexLine&,
+                              FlexLine*,
                               LayoutUnit initial_free_space,
                               LayoutUnit& remaining_free_space);
   void FreezeViolations(Vector<FlexItem*>&,
@@ -215,7 +215,7 @@ class CORE_EXPORT LayoutFlexibleBox : public LayoutBlock {
                                               LayoutUnit child_preferred_size);
   void PrepareChildForPositionedLayout(LayoutBox& child);
   void LayoutAndPlaceChildren(LayoutUnit& cross_axis_offset,
-                              FlexLine&,
+                              FlexLine*,
                               LayoutUnit available_free_space,
                               bool relayout_children,
                               SubtreeLayoutScope&);