[LayoutNG] Remove the state machine from ng_out_of_flow_layout_part.

third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/layout/ng/ng_block_layout_algorithm.h"
 
 #include "core/layout/ng/ng_box_fragment.h"
 #include "core/layout/ng/ng_break_token.h"
 #include "core/layout/ng/ng_constraint_space.h"
 #include "core/layout/ng/ng_constraint_space_builder.h"
@@ skipping 356 matching lines @@
     fragment_offset = PositionFloatFragment(*fragment, child_margins);
   } else {
     ApplyAutoMargins(*space_for_current_child_, CurrentChildStyle(), *fragment,
                      &child_margins);
     fragment_offset = PositionFragment(*fragment, child_margins);
   }
   builder_->AddChild(fragment, fragment_offset);
 }
 
 bool NGBlockLayoutAlgorithm::LayoutOutOfFlowChild() {
-  if (!current_child_) {
-    if (out_of_flow_candidates_.isEmpty()) {
-      out_of_flow_layout_ = nullptr;
-      out_of_flow_candidate_positions_.clear();
-      return true;
-    }
-    current_child_ = out_of_flow_candidates_.first();
-    out_of_flow_candidates_.removeFirst();
-    NGStaticPosition position = out_of_flow_candidate_positions_
-        [out_of_flow_candidate_positions_index_++];
+  if (out_of_flow_candidates_.isEmpty()) {
+    out_of_flow_layout_ = nullptr;
+    out_of_flow_candidate_positions_.clear();
+    return true;
+  }
+  current_child_ = out_of_flow_candidates_.first();
+  out_of_flow_candidates_.removeFirst();
+  NGStaticPosition static_position = out_of_flow_candidate_positions_
+      [out_of_flow_candidate_positions_index_++];
 
-    if (!out_of_flow_layout_->StartLayout(current_child_, position)) {
-      builder_->AddOutOfFlowDescendant(current_child_, position);
-      current_child_ = nullptr;
-      return false;
-    }
-  }
-  NGFragment* fragment;
-  NGLogicalOffset offset;
-  if (out_of_flow_layout_->Layout(&fragment, &offset) == kNewFragment) {
+  EPosition position = current_child_->Style()->position();
+  bool contains_fixed = Style().canContainFixedPositionObjects();
+  bool contains_absolute =
+      Style().canContainAbsolutePositionObjects() || contains_fixed;
+
+  if ((contains_absolute && position == AbsolutePosition) ||
+      (contains_fixed && position == FixedPosition)) {
+    NGFragment* fragment;
+    NGLogicalOffset offset;
+    out_of_flow_layout_->Layout(*current_child_, static_position, &fragment,
+                                &offset);
     // TODO(atotic) Need to adjust size of overflow rect per spec.

[atotic, 2017/01/18 18:48:49]

I think the code to decide whether NGBlockNode can be positioned by
NGOutOfFlowPart should remain a method of NGOutOfFlowPart. The reason is code
reuse:
- there will be other callers of NGOutOfFlowPart. All of these would have to
replicate this logic.
- the code to be reused is non-trivial, and might change in the future.

[ikilpatrick, 2017/01/18 19:32:13]

Right, I've pulled it into a static method inside ng_absolute_utils. It may be
easier to pull some of this into the LayoutPart now that we are removing the
state machine.

I didn't add it back into the LayoutPart yet as it makes it confusing as to what
is if-branch is doing. 

     builder_->AddChild(fragment, offset);
-    current_child_ = nullptr;
+  } else {
+    builder_->AddOutOfFlowDescendant(current_child_, static_position);
   }
+
   return false;
 }
 
 NGBoxStrut NGBlockLayoutAlgorithm::CollapseMargins(
     const NGBoxStrut& margins,
     const NGBoxFragment& fragment) {
   bool is_zero_height_box = !fragment.BlockSize() && margins.IsEmpty() &&
                             fragment.MarginStrut().IsEmpty();
   // Create the current child's margin strut from its children's margin strut or
   // use margin strut from the the last non-empty child.
@@ skipping 148 matching lines @@
   visitor->trace(builder_);
   visitor->trace(space_builder_);
   visitor->trace(space_for_current_child_);
   visitor->trace(current_child_);
   visitor->trace(current_minmax_child_);
   visitor->trace(out_of_flow_layout_);
   visitor->trace(out_of_flow_candidates_);
 }
 
 }  // namespace blink