Calculate positioningArea and not just size, for tiling background.

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

Index: third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp
diff --git a/third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp b/third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp
index c6c2fb012185c9044f448af1ed6d33fde383bb05..d9c2b1bb690abca582abc5959f5f951b040da350 100644
--- a/third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp
+++ b/third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp
@@ -411,7 +411,7 @@ void BackgroundImageGeometry::calculate(
     const LayoutRect& paintRect) {
   LayoutUnit left;
   LayoutUnit top;
-  LayoutSize positioningAreaSize;
+  LayoutRect positioningArea;
   bool isLayoutView = obj.isLayoutView();
   const LayoutBox* rootBox = nullptr;
   if (isLayoutView) {
@@ -473,8 +473,9 @@ void BackgroundImageGeometry::calculate(
       // The background of the box generated by the root element covers the
       // entire canvas and will be painted by the view object, but the we should
       // still use the root element box for positioning.
-      positioningAreaSize =
-          rootBox->size() - LayoutSize(left + right, top + bottom);
+      positioningArea.setSize(rootBox->size());
+      positioningArea.contractEdges(top, right, bottom, left);
+
       // The input paint rect is specified in root element local coordinate
       // (i.e. a transform is applied on the context for painting), and is
       // expanded to cover the whole canvas.  Since left/top is relative to the
@@ -482,12 +483,14 @@ void BackgroundImageGeometry::calculate(
       left -= paintRect.x();
       top -= paintRect.y();
     } else {
-      positioningAreaSize =
-          (cellUsingContainerBackground
-               ? getBackgroundObjectDimensions(toLayoutTableCell(obj),
-                                               toLayoutBox(positioningBox))
-               : paintRect.size()) -
-          LayoutSize(left + right, top + bottom);
+      if (cellUsingContainerBackground) {
+        positioningArea.setSize(getBackgroundObjectDimensions(
+            toLayoutTableCell(obj), toLayoutBox(positioningBox)));
+      } else {
+        positioningArea = paintRect;
+      }
+
+      positioningArea.contractEdges(top, right, bottom, left);
     }
   } else {
     setHasNonLocalGeometry();
@@ -509,11 +512,11 @@ void BackgroundImageGeometry::calculate(
           LayoutPoint(-paintContainer->localToAbsolute(FloatPoint())));
 
     setDestRect(viewportRect);
-    positioningAreaSize = destRect().size();
+    positioningArea = viewportRect;
   }
 
   LayoutSize fillTileSize(
-      calculateFillTileSize(positioningBox, fillLayer, positioningAreaSize));
+      calculateFillTileSize(positioningBox, fillLayer, positioningArea.size()));
   // It's necessary to apply the heuristic here prior to any further
   // calculations to avoid incorrectly using sub-pixel values that won't be
   // present in the painted tile.
@@ -522,12 +525,12 @@ void BackgroundImageGeometry::calculate(
   EFillRepeat backgroundRepeatX = fillLayer.repeatX();
   EFillRepeat backgroundRepeatY = fillLayer.repeatY();
   LayoutUnit unsnappedAvailableWidth =
-      positioningAreaSize.width() - fillTileSize.width();
+      positioningArea.width() - fillTileSize.width();
   LayoutUnit unsnappedAvailableHeight =
-      positioningAreaSize.height() - fillTileSize.height();
-  positioningAreaSize =
-      LayoutSize(snapSizeToPixel(positioningAreaSize.width(), m_destRect.x()),
-                 snapSizeToPixel(positioningAreaSize.height(), m_destRect.y()));
+      positioningArea.height() - fillTileSize.height();
+  LayoutSize positioningAreaSize =
+      LayoutSize(snapSizeToPixel(positioningArea.width(), m_destRect.x()),
+                 snapSizeToPixel(positioningArea.height(), m_destRect.y()));
   LayoutUnit availableWidth = positioningAreaSize.width() - tileSize().width();
   LayoutUnit availableHeight =
       positioningAreaSize.height() - tileSize().height();