[layoutng] async layout part 1: Change the API to support async

third_party/WebKit/Source/core/layout/ng/ng_box.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_box.h"
 
 #include "core/layout/LayoutObject.h"
 #include "core/layout/ng/layout_ng_block_flow.h"
 #include "core/layout/ng/ng_block_layout_algorithm.h"
 #include "core/layout/ng/ng_box_iterator.h"
 #include "core/layout/ng/ng_constraint_space.h"
 #include "core/layout/ng/ng_fragment.h"
 #include "core/layout/ng/ng_fragment_builder.h"
 #include "core/layout/ng/ng_writing_mode.h"
 #include "core/layout/LayoutBlockFlow.h"
 #include "core/layout/LayoutBox.h"
 
 namespace blink {
 
-NGFragment* NGBox::layout(const NGConstraintSpace* constraint_space) {
+bool NGBox::Layout(const NGConstraintSpace* constraint_space,
+                   NGFragment** out) {
   // We can either use the new layout code to do the layout and then copy the
   // resulting size to the LayoutObject, or use the old layout code and
   // synthesize a fragment.
   NGFragment* fragment = nullptr;
   if (canUseNewLayout()) {
     NGBlockLayoutAlgorithm algorithm(style(), childIterator());
 
     // Change the coordinate system of the constraint space.
     NGConstraintSpace* child_constraint_space = new NGConstraintSpace(
         FromPlatformWritingMode(style()->getWritingMode()), constraint_space);
 
-    fragment = algorithm.layout(child_constraint_space);
+    if (!algorithm.Layout(child_constraint_space, &fragment))
+      return false;
     m_layoutBox->setLogicalWidth(fragment->InlineSize());
     m_layoutBox->setLogicalHeight(fragment->BlockSize());
     if (m_layoutBox->isLayoutBlock())
       toLayoutBlock(m_layoutBox)->layoutPositionedObjects(true);
     m_layoutBox->clearNeedsLayout();
   } else {
     // TODO(layout-ng): If fixedSize is true, set the override width/height too
     NGLogicalSize container_size = constraint_space->ContainerSize();
     m_layoutBox->setOverrideContainingBlockContentLogicalWidth(
         container_size.inline_size);
     m_layoutBox->setOverrideContainingBlockContentLogicalHeight(
         container_size.block_size);
     if (m_layoutBox->isLayoutNGBlockFlow() && m_layoutBox->needsLayout()) {
       toLayoutNGBlockFlow(m_layoutBox)->LayoutBlockFlow::layoutBlock(true);
     } else {
       m_layoutBox->layoutIfNeeded();
     }
     LayoutRect overflow = m_layoutBox->layoutOverflowRect();
     // TODO(layout-ng): This does not handle writing modes correctly (for
     // overflow & the enums)
     NGFragmentBuilder builder(NGFragmentBase::FragmentBox);
     builder.SetInlineSize(m_layoutBox->logicalWidth())
         .SetBlockSize(m_layoutBox->logicalHeight())
         .SetInlineOverflow(overflow.width())
         .SetBlockOverflow(overflow.height());
     fragment = builder.ToFragment();
   }
-  return fragment;
+  *out = fragment;
+  return true;
 }
 
 const ComputedStyle* NGBox::style() const {
   return m_layoutBox->style();
 }
 
 NGBoxIterator NGBox::childIterator() {
   return NGBoxIterator(firstChild());
 }
 
@@ skipping 11 matching lines @@
 }
 
 bool NGBox::canUseNewLayout() {
   if (!m_layoutBox)
     return true;
   if (m_layoutBox->isLayoutBlockFlow() && !m_layoutBox->childrenInline())
     return true;
   return false;
 }
 }  // namespace blink