Fix paint invalidation of paintInvalidationContainer itself

third_party/WebKit/Source/core/layout/LayoutBox.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.cpp b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
index c48220c9b982670f937e3d025d61a06373815254..6aabf0e865c2358a2804e8e3321c29c741392b87 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -1901,6 +1901,12 @@ void LayoutBox::mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* ance
     // included into the visual overflow for repaint, we wouldn't have this issue.
     inflatePaintInvalidationRectForReflectionAndFilter(rect);
 
+    if (ancestor == this) {

[chrishtr, 2016/03/11 21:17:16]

This seems fragile. Can it just be moved down into
PaintInvalidationState::canMapToContainer?

[Xianzhu, 2016/03/11 21:39:56]

This code is also needed when there is no paintInvalidationState, so we can't
move it into PaintInvalidationState::canMapToContainer() which is only called
when there is paintInvalidationContainer.

In next steps for new paint invalidation, I plan to add
PaintInvalidationState::mapObjectRectToAncestor() to include the code below from
1910 to 1922, and remove PaintInvalidationState parameter from this function,
and let PaintInvalidationState::mapObjectRectToAncestor() fallback to this
function if fast mapping is not possible.

[chrishtr, 2016/03/11 21:43:06]

Ok. Please add a comment explaining then.

[Xianzhu, 2016/03/11 22:08:25]

Done.

[chrishtr, 2016/03/11 22:11:44]

Actually, hold on a minute. would it be cleaner and just as forward compatible
to leave the lines 1919-1923 you're deleting and implement the
PaintInvalidationContainer logic I suggested?

[Xianzhu, 2016/03/11 22:23:43]

I don't quite understand your suggestion. Do you mean to move 'ancestor == this'
condition into canMapToContainer() and let it return false for the condition, or
to move the whole block 1904-1908 into it? The latter is not feasible because we
also need the block for non-paintInvalidationState case.

+        if (ancestor->style()->isFlippedBlocksWritingMode())
+            flipForWritingMode(rect);
+        return;
+    }
+
     if (paintInvalidationState && paintInvalidationState->canMapToContainer(ancestor) && position != FixedPosition) {
         if (layer() && layer()->transform())
             rect = LayoutRect(layer()->transform()->mapRect(pixelSnappedIntRect(rect)));
@@ -1916,12 +1922,6 @@ void LayoutBox::mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* ance
         return;
     }
 
-    if (ancestor == this) {
-        if (ancestor->style()->isFlippedBlocksWritingMode())
-            flipForWritingMode(rect);
-        return;
-    }
-
     bool containerSkipped;
     LayoutObject* container = this->container(ancestor, &containerSkipped);
     if (!container)