Fix paint invalidation for composited vertical-rl having overflow

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

Index: third_party/WebKit/Source/core/layout/LayoutView.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutView.cpp b/third_party/WebKit/Source/core/layout/LayoutView.cpp
index bb9eb0ea9d9fd927f44b756ad3b2879672bcff85..5f2e63ffb59b399eb8677ce5c99af321db720876 100644
--- a/third_party/WebKit/Source/core/layout/LayoutView.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutView.cpp
@@ -294,7 +294,9 @@ LayoutRect LayoutView::visualOverflowRect() const
     // In normal compositing mode, LayoutView doesn't actually apply clipping
     // on its descendants. Instead their visual overflow is propagated to
     // compositor()->m_rootContentLayer for accelerated scrolling.
-    return LayoutRect(documentRect());

[chrishtr, 2016/09/27 00:02:43]

Why not just return layoutOverflowRect() here? This avoids double-flipping and
the pixel snapping in documentRect().
Also the pixel snapping in documentRect() looks incorrect. The call sites to it
should I think be adjusted to flow
subpixel positioning through and snap at the end. e.g.:

https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/layout/co...

is not adding up the subpixelAccumulation before snapping.

[Xianzhu, 2016/09/27 00:26:45]

Good idea. Should have looked into documentRect().

Done.

+    LayoutRect rect(documentRect());
+    flipForWritingMode(rect);
+    return rect;
 }
 
 LayoutRect LayoutView::localOverflowRectForPaintInvalidation() const