Support edge-inclusive intersections in mapToVisibleRectInAncestorSpace

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

Index: third_party/WebKit/Source/core/layout/LayoutBox.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.h b/third_party/WebKit/Source/core/layout/LayoutBox.h
index 007845e72fff036449020792a49f33fb7ac9398c..c3098369cd0e71a21d13839bebd89ce8ccab17a8 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.h
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.h
@@ -639,7 +639,7 @@ public:
     bool hasForcedBreakAfter() const;
 
     LayoutRect clippedOverflowRectForPaintInvalidation(const LayoutBoxModelObject* paintInvalidationContainer, const PaintInvalidationState* = nullptr) const override;
-    void mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* ancestor, LayoutRect&, const PaintInvalidationState*) const override;
+    bool mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* ancestor, LayoutRect&, const PaintInvalidationState*, VisibleRectFlags = DefaultVisibleRectFlags) const override;
     virtual void invalidatePaintForOverhangingFloats(bool paintAllDescendants);
 
     LayoutUnit containingBlockLogicalHeightForGetComputedStyle() const;
@@ -842,7 +842,11 @@ public:
 
     IntSize scrolledContentOffset() const;
     void mapScrollingContentsRectToBoxSpace(LayoutRect&) const;
-    void applyOverflowClip(LayoutRect&) const;
+
+    // Returns true if the rect actually intersects the clipping region.

[chrishtr, 2016/03/22 19:54:26]

Add a comment that this is not an "iff" - i.e. there may be false positives.

[szager1, 2016/03/23 23:26:59]

I don't think that's true.  applyOverflowClip always calls either
LayoutRect::intersect or LayoutRect::inclusiveIntersect, and the return value is
set on basis of that call.  If this method returns 'true', it must be the case
that the argument rect actually intersects the clip region.

[chrishtr, 2016/03/24 21:18:43]

Ok you win. :)

+    // If edgeInclusive is true, then this method may return true even
+    // if the resulting rect has zero area.
+    bool applyOverflowClip(LayoutRect&, VisibleRectFlags = DefaultVisibleRectFlags) const;
 
     virtual bool hasRelativeLogicalWidth() const;
     virtual bool hasRelativeLogicalHeight() const;