Disallow fragmentation of composited content.

third_party/WebKit/Source/core/paint/PaintLayer.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index c0eaf2464ad1ce073a4a366da2c551bb78b58b94..ff034153c96cca5600474eb76b4d0b542e8f5f5f 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -1490,6 +1490,11 @@ void PaintLayer::appendSingleFragmentIgnoringPagination(PaintLayerFragments& fra
     fragments.append(fragment);
 }
 
+bool PaintLayer::shouldFragmentCompositedBounds(const PaintLayer* compositingLayer) const
+{
+    return enclosingPaginationLayer() && !compositingLayer->enclosingPaginationLayer();

[wkorman, 2016/06/02 18:04:15]

Considering whether a comment to explain this further is warranted here or
elsewhere, re:

https://groups.google.com/a/chromium.org/d/msg/paint-dev/uQF-DlRlf1k/EDXipWUO...

[chrishtr, 2016/06/02 18:22:43]

Done.

+}
+
 void PaintLayer::collectFragments(PaintLayerFragments& fragments, const PaintLayer* rootLayer, const LayoutRect& dirtyRect,
     ClipRectsCacheSlot clipRectsCacheSlot, OverlayScrollbarClipBehavior overlayScrollbarClipBehavior, ShouldRespectOverflowClipType respectOverflowClip, const LayoutPoint* offsetFromRoot,
     const LayoutSize& subPixelAccumulation, const LayoutRect* layerBoundingBox)
@@ -1500,6 +1505,11 @@ void PaintLayer::collectFragments(PaintLayerFragments& fragments, const PaintLay
         return;
     }
 
+    if (!shouldFragmentCompositedBounds(rootLayer)) {
+        appendSingleFragmentIgnoringPagination(fragments, rootLayer, dirtyRect, clipRectsCacheSlot, overlayScrollbarClipBehavior, respectOverflowClip, offsetFromRoot, subPixelAccumulation);
+        return;
+    }
+
     // Compute our offset within the enclosing pagination layer.
     LayoutPoint offsetWithinPaginatedLayer;
     convertToLayerCoords(enclosingPaginationLayer(), offsetWithinPaginatedLayer);
@@ -2253,7 +2263,7 @@ LayoutRect PaintLayer::boundingBoxForCompositing(const PaintLayer* ancestorLayer
     if (transform() && paintsWithTransform(GlobalPaintNormalPhase) && (this != ancestorLayer || options == MaybeIncludeTransformForAncestorLayer))
         result = transform()->mapRect(result);
 
-    if (enclosingPaginationLayer()) {
+    if (shouldFragmentCompositedBounds(ancestorLayer)) {
         convertFromFlowThreadToVisualBoundingBoxInAncestor(ancestorLayer, result);
         return result;
     }