Combine LayoutObject::previousPaintOffset and paintOffset in paint properties

third_party/WebKit/Source/core/layout/LayoutObject.h

Index: third_party/WebKit/Source/core/layout/LayoutObject.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.h b/third_party/WebKit/Source/core/layout/LayoutObject.h
index 82075ad1ed24a2aa9211a8441f7cc133f7729b22..3134b8cd6188312125fe188109acf6d62e4e9fd5 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.h
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.h
@@ -1575,9 +1575,7 @@ class CORE_EXPORT LayoutObject : public ImageResourceObserver,
   // Called when the previous visual rect(s) is no longer valid.
   virtual void clearPreviousVisualRects();
 
-  const LayoutPoint& previousPaintOffset() const {
-    return m_previousPaintOffset;
-  }
+  const LayoutPoint& paintOffset() const { return m_paintOffset; }
 
   PaintInvalidationReason fullPaintInvalidationReason() const {
     return m_bitfields.fullPaintInvalidationReason();
@@ -1679,9 +1677,9 @@ class CORE_EXPORT LayoutObject : public ImageResourceObserver,
     void setPreviousVisualRect(const LayoutRect& r) {
       m_layoutObject.setPreviousVisualRect(r);
     }
-    void setPreviousPaintOffset(const LayoutPoint& p) {
+    void setPaintOffset(const LayoutPoint& p) {

[Xianzhu, 2017/01/06 17:24:39]

Drop "Previous" because we also use paintOffset() in the same cycle and
previousPaintOffset() would confuse in the situation.

Would also like to drop other "previous"s in e.g. previousVisualRect because
they have the same situation.

We could alternatively use 'Last' instead of 'Previous'. Would like to hear your
opinions.

[pdr., 2017/01/06 18:27:42]

I like these renames.

Can you add a comment like so:
// Store the current paint offset as calculated during the pre-paint tree walk.
And an assert here that this is only called during InPrePaint?

Similarly for paintOffset(), can you add a comment like so:
// Paint offset as calculated in the pre-paint tree walk.
And an assert that it is only accessed in or after PrePaint?

[Xianzhu, 2017/01/06 19:24:18]

Done.

       DCHECK(RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled());
-      m_layoutObject.m_previousPaintOffset = p;
+      m_layoutObject.m_paintOffset = p;
     }
     void setHasPreviousLocationInBacking(bool b) {
       m_layoutObject.m_bitfields.setHasPreviousLocationInBacking(b);
@@ -2445,7 +2443,7 @@ class CORE_EXPORT LayoutObject : public ImageResourceObserver,
   // offset that will be used to paint the object on SPv2. It's used to detect

[pdr., 2017/01/06 18:27:42]

This comment is a little out of date. Can you update it?

[Xianzhu, 2017/01/06 19:24:18]

Can you point out the out of date part?

For paint invalidation and painting it still applies for SPv2 only because the
paint offset used in painting on SPv1 is sometimes different because of paint
invalidation containers.

[pdr., 2017/01/06 19:40:01]

You're right, this is up to date.

   // paint offset change for paint invalidation on SPv2, and partial paint
   // property tree update for SlimmingPaintInvalidation on SPv1 and SPv2.
-  LayoutPoint m_previousPaintOffset;
+  LayoutPoint m_paintOffset;
 
   // For SPv2 only. The ObjectPaintProperties structure holds references to the
   // property tree nodes that are created by the layout object for painting.