[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

[eae, 2016/10/25 17:26:27]

Should this be PhysicalConstraintSpaceBuilder? Also do we really need a builder
for this given that we expect most constraint spaces to share a
NGPhysicalConstraintSpace.
For NGConstraintSpace I clearly see the need but for NGPhysicalConstraintSpace?
Not quite as clear-cut.

[ikilpatrick, 2016/10/25 23:20:42]

Can rename to that; was following ng_fragment_builder which also returns a
PhysicalFragment; up to you :).

[ikilpatrick, 2016/10/25 23:20:42]

Right, yeah there are more cases than I originally thought when we are going to
need to change the constraint space for a child. I.e.

Est. new formatting context (eventually should be moved to style, but complex
due to multi-col),
Inside fragmentation context (where to fragment depends on your siblings
position).
Size is determined by parent.

I could add a bool on this like "has_changed_" which if false, just returns the
previous space?

+    : public GarbageCollectedFinalized<NGConstraintSpaceBuilder> {

[Gleb Lanbin, 2016/10/25 17:37:27]

.nit you don't have anything that needs to be finalized here. just
GarbageCollected

[ikilpatrick, 2016/10/25 23:20:42]

Done.

+ public:
+  NGConstraintSpaceBuilder(NGWritingMode writing_mode);
+
+  NGConstraintSpaceBuilder& SetContainerSize(NGLogicalSize container_size);
+  NGConstraintSpaceBuilder& SetFixedSize(bool fixed_inline, bool fixed_block);
+  NGConstraintSpaceBuilder& SetOverflowTriggersScrollbar(
+      bool inline_direction_triggers_scrollbar,
+      bool block_direction_triggers_scrollbar);
+  NGConstraintSpaceBuilder& SetFragmentationType(NGFragmentationType);

[Gleb Lanbin, 2016/10/25 17:37:27]

Can we use SetFragmentType here and have a TODO to rename NGFragmentationType to
NGFragmentType

[ikilpatrick, 2016/10/25 23:20:42]

FragmentationType and FragmentType are different, (currently not using
FragmentationType yet).

It might be better named FragmentationBreakType? See fragmentation break in:
https://drafts.csswg.org/css-break/

Thoughts?

+  NGConstraintSpaceBuilder& SetIsNewFormattingContext(bool is_new_fc);
+
+  // Creates a new constraint space. Can be called multiple times.

[Gleb Lanbin, 2016/10/25 17:37:27]

can you provide a bit more details here about why it's expected to be called
multiple times, how those constraint spaces are different from each other.

[ikilpatrick, 2016/10/25 23:20:42]

Done.

+  NGPhysicalConstraintSpace* ToConstraintSpace();
+
+  DEFINE_INLINE_TRACE() {}
+
+ private:
+  NGLogicalSize container_size_;
+
+  unsigned writing_mode_ : 2;

[Gleb Lanbin, 2016/10/25 17:37:27]

should we separate mutable fields from const fields?
// const bit fields.
const unsigned writing_mode_ : 2;
const unsigned fixed_inline_ : 1;

// mutable bit fields.
unsigned inline_direction_triggers_scrollbar_ : 1;
unsigned block_direction_triggers_scrollbar_ : 1;

[ikilpatrick, 2016/10/25 23:20:42]

Done.

+  unsigned fixed_inline_ : 1;
+  unsigned fixed_block_ : 1;
+  unsigned inline_direction_triggers_scrollbar_ : 1;
+  unsigned block_direction_triggers_scrollbar_ : 1;
+  unsigned fragmentation_type_ : 2;

[Gleb Lanbin, 2016/10/25 17:37:27]

.nit fragment_type_ ?

[ikilpatrick, 2016/10/25 23:20:42]

See above.

+  unsigned is_new_fc_ : 1;
+};
+
+}  // namespace blink
+
+#endif  // NGConstraintSpaceBuilder