InPrePaint document state and PrePaintTreeWalk class

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

Index: third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h
diff --git a/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h b/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h
new file mode 100644
index 0000000000000000000000000000000000000000..7868982a8748c6976212bbcf11c68e17dec46355
--- /dev/null
+++ b/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h
@@ -0,0 +1,32 @@
+// 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 PrePaintTreeWalk_h
+#define PrePaintTreeWalk_h
+
+#include "core/paint/PaintPropertyTreeBuilder.h"
+
+namespace blink {
+
+class FrameView;
+class LayoutObject;
+struct PrePaintTreeWalkContext;
+
+// This class walks the whole layout tree, beginning from the root FrameView, across
+// frame boundaries. Helper classes are called for each tree node to perform actual actions.
+// It expects to be invoked in InPrePaint phase.
+class PrePaintTreeWalk {
+public:
+    void walk(FrameView& rootFrame);

[pdr., 2016/05/31 23:17:39]

Nit: const FrameView&?

[Xianzhu, 2016/05/31 23:41:40]

FrameView doesn't have getMutableForPainting() and we need to call its non-const
methods (setPreTranslation() etc.)

We could consider the same mechanism to isolate mutations from painting, but
this seems not a big deal because FrameView's status is much simpler that that
of LayoutObjects.

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

[pdr., 2016/05/31 23:17:39]

Nit: const FrameView&?

+    void walk(const LayoutObject&, const PrePaintTreeWalkContext&);
+
+    PaintPropertyTreeBuilder m_propertyTreeBuilder;
+};
+
+} // namespace blink
+
+#endif // PrePaintTreeWalk_h