[SPv2] Track paint offset change

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

 // Copyright 2014 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 ObjectPainter_h
 #define ObjectPainter_h
 
 #include "core/style/ComputedStyleConstants.h"
 #include "wtf/Allocator.h"
 #include "wtf/Vector.h"
@@ skipping 42 matching lines @@
   // Also see core/paint/README.md.
   //
   // It is expected that the caller will call this function independent of the
   // value of paintInfo.phase, and this function will do atomic paint (for
   // PaintPhaseForeground), normal paint (for PaintPhaseSelection and
   // PaintPhaseTextClip) or nothing (other paint phases) according to
   // paintInfo.phase.
   void paintAllPhasesAtomically(const PaintInfo&,
                                 const LayoutPoint& paintOffset);
 
+  void checkPaintOffset(const PaintInfo& paintInfo,

[pdr., 2016/11/10 07:35:32]

Add a comment here:
// SPV2 computes paint offsets during the prepaint tree
// walk (PrePaintTreeWalk). This check verifies that the
// SPV1 paint offset computed during paint matches the
// new SPV2 paint offset.


WDYT about making it more clear at the callsites that this is spv2 debug code?
It's a little verbose but maybe something like:
if (RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
  DCHECK(ObjectPainter(m_whatever).paintOffsetPrecomputed(paintInfo,
paintOffset));
}

[Xianzhu, 2016/11/10 17:41:10]

Done.
I like the clearness. How about the new patch that moved the checking in header
file?

[pdr., 2016/11/10 18:54:11]

SGTM. Followups are always great.

+                        const LayoutPoint& paintOffset) {
+#if DCHECK_IS_ON()
+    doCheckPaintOffset(paintInfo, paintOffset);
+#endif
+  }
+
  private:
   static void drawDashedOrDottedBoxSide(GraphicsContext&,
                                         int x1,
                                         int y1,
                                         int x2,
                                         int y2,
                                         BoxSide,
                                         Color,
                                         int thickness,
                                         EBorderStyle,
@@ skipping 25 matching lines @@
                                int x1,
                                int y1,
                                int x2,
                                int y2,
                                BoxSide,
                                Color,
                                int adjacentWidth1,
                                int adjacentWidth2,
                                bool antialias);
 
+#if DCHECK_IS_ON()
+  void doCheckPaintOffset(const PaintInfo&, const LayoutPoint& paintOffset);
+#endif
+
   const LayoutObject& m_layoutObject;
 };
 
 }  // namespace blink
 
 #endif