Preliminary paint property walk implementation for SPv2

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h

Index: third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h
diff --git a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h
new file mode 100644
index 0000000000000000000000000000000000000000..88c4367ea495c843005242acbddff5104fa8163f
--- /dev/null
+++ b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h
@@ -0,0 +1,28 @@
+// Copyright 2015 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 PaintPropertyTreeBuilder_h
+#define PaintPropertyTreeBuilder_h
+
+namespace blink {
+
+class FrameView;
+class LayoutBoxModelObject;
+class LayoutObject;

[pdr., 2015/10/20 22:02:31]

"class LayoutObject" and "struct PaintPropertyTreeNode" aren't needed.

[trchen, 2015/10/21 06:16:20]

Done.

+struct PaintPropertyTreeNode;
+
+class PaintPropertyTreeBuilder {

[jbroman, 2015/10/20 23:50:13]

Class comment please. At least a description that this class walks the layout
tree in XYZ order and builds paint properties, etc.

[trchen, 2015/10/21 06:16:20]

I consider the walk ordering being implementation details. Let's add comments in
.cpp. But indeed, it worth mention that it walks the whole layout tree, from the
root frame, across frame boundaries (not implemented yet, but will be).

+public:
+    void buildPropertyTrees(FrameView& rootFrame);

[pdr., 2015/10/20 22:02:31]

WDYT about making all of these functions const since they only modify their in
param?

[jbroman, 2015/10/20 23:50:13]

IMHO either these are (potentially) stateful objects (in which case it's
appropriate for the methods to be non-const), or they aren't going to be
stateful in the future (in which case it should be a function).

[trchen, 2015/10/21 06:16:20]

Yep, I feel that it is very likely to become stateful.

+
+private:
+    struct Context;
+
+    void walk(FrameView&, const Context&);

[pdr., 2015/10/20 22:02:31]

Can you doc which tree traversal order is used in this walk? (layout object tree
order, not paint order).

[trchen, 2015/10/21 06:16:20]

Ditto.

+    void walk(LayoutBoxModelObject&, const Context&);
+};
+
+} // namespace blink
+
+#endif // PaintPropertyTreeBuilder_h