[LayoutNG] Add NGConstraintSpaceBuilder class.

third_party/WebKit/Source/core/layout/ng/ng_constraint_space_builder.h

+// 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.
+
+#ifndef NGConstraintSpaceBuilder_h
+#define NGConstraintSpaceBuilder_h
+
+#include "core/layout/ng/ng_fragment.h"
+#include "core/layout/ng/ng_units.h"
+
+namespace blink {
+
+class CORE_EXPORT NGConstraintSpaceBuilder final
+    : public GarbageCollected<NGConstraintSpaceBuilder> {
+ public:
+  NGConstraintSpaceBuilder(NGWritingMode writing_mode);
+
+  NGConstraintSpaceBuilder& SetContainerSize(NGLogicalSize container_size);
+  NGConstraintSpaceBuilder& SetFixedSize(bool fixed_inline, bool fixed_block);

[Gleb Lanbin, 2016/10/26 18:22:14]

you don't need to do this in this patch but lets split this and other methods
below for readability sake, i.e.

NGConstraintSpaceBuilder& SetIsFixedSizeInline(bool is_fixed_size_inline) {
  this.is_fixed_size_inline = is_fixed_size_inline
}

please compare the old and new version
OLD
NGConstraintSpaceBuilder builder;
// It's not clear what we're setting to true/false here.
builder.SetFixedSize(true, false); 

NEW
NGConstraintSpaceBuilder builder;
builder
   .SetIsFixedSizeInline(true)
   .SetIsFixedSizeBlock(true);

also I recommend to use IS prefix, this is because SetFixedSize sounds like
we're setting a fixed size, rectangle or something but in reality we want to set
some options.

[ikilpatrick, 2016/10/26 18:56:35]

^ sgtm.

+  NGConstraintSpaceBuilder& SetOverflowTriggersScrollbar(
+      bool inline_direction_triggers_scrollbar,
+      bool block_direction_triggers_scrollbar);
+  NGConstraintSpaceBuilder& SetFragmentationType(NGFragmentationType);
+  NGConstraintSpaceBuilder& SetIsNewFormattingContext(bool is_new_fc);
+
+  // Creates a new constraint space. This may be called multiple times, for
+  // example the constraint space will be different for a child which:
+  //  - Establishes a new formatting context.
+  //  - Is within a fragmentation container and needs its fragmentation offset
+  //    updated.
+  //  - Has its size is determined by its parent layout (flex, abs-pos).
+  NGPhysicalConstraintSpace* ToConstraintSpace();
+
+  DEFINE_INLINE_TRACE() {}
+
+ private:
+  NGLogicalSize container_size_;
+
+  // const bit fields.
+  const unsigned writing_mode_ : 2;
+
+  // mutable bit fields.
+  unsigned fixed_inline_ : 1;
+  unsigned fixed_block_ : 1;
+  unsigned inline_direction_triggers_scrollbar_ : 1;
+  unsigned block_direction_triggers_scrollbar_ : 1;
+  unsigned fragmentation_type_ : 2;
+  unsigned is_new_fc_ : 1;
+};
+
+}  // namespace blink
+
+#endif  // NGConstraintSpaceBuilder