Background image should clamp to minimum size(1, 1) after scale.

Source/core/paint/BoxPainter.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/paint/BoxPainter.h"
 
 #include "core/HTMLNames.h"
 #include "core/frame/Settings.h"
 #include "core/html/HTMLFrameOwnerElement.h"
@@ skipping 806 matching lines @@
         if (layerWidth.isFixed())
             tileSize.setWidth(layerWidth.value());
         else if (layerWidth.isPercent())
             tileSize.setWidth(valueForLength(layerWidth, positioningAreaSize.width()));
 
         if (layerHeight.isFixed())
             tileSize.setHeight(layerHeight.value());
         else if (layerHeight.isPercent())
             tileSize.setHeight(valueForLength(layerHeight, positioningAreaSize.height()));
 
         applySubPixelHeuristicForTileSize(tileSize, positioningAreaSize);

[chrishtr, 2014/10/17 19:02:17]

How about moving applySubPixelHeuristicForTileSize down to line 841? I think it
will fix the issue in this bug. Not sure if it has other side-effects, could you
please check by running the layout tests?

 
         // If one of the values is auto we have to use the appropriate
         // scale to maintain our aspect ratio.
         if (layerWidth.isAuto() && !layerHeight.isAuto()) {
             if (imageIntrinsicSize.height())
                 tileSize.setWidth(imageIntrinsicSize.width() * tileSize.height() / imageIntrinsicSize.height());
         } else if (!layerWidth.isAuto() && layerHeight.isAuto()) {
             if (imageIntrinsicSize.width())
                 tileSize.setHeight(imageIntrinsicSize.height() * tileSize.width() / imageIntrinsicSize.width());
         } else if (layerWidth.isAuto() && layerHeight.isAuto()) {
             // If both width and height are auto, use the image's intrinsic size.
             tileSize = imageIntrinsicSize;
         }
 
-        tileSize.clampNegativeToZero();
+        tileSize.clampToMinimumSize(IntSize(1, 1));
         return flooredIntSize(tileSize);
     }
     case SizeNone: {
         // If both values are ‘auto’ then the intrinsic width and/or height of the image should be used, if any.
         if (!imageIntrinsicSize.isEmpty())
             return imageIntrinsicSize;
 
         // If the image has neither an intrinsic width nor an intrinsic height, its size is determined as for ‘contain’.
         type = Contain;
     }
@@ skipping 1293 matching lines @@
 
     FloatPoint secondQuad[4];
     secondQuad[0] = quad[0];
     secondQuad[1] = FloatPoint(quad[0].x() - r1 * cx, quad[0].y() - r1 * cy);
     secondQuad[2] = quad[2];
     secondQuad[3] = quad[3];
     graphicsContext->clipConvexPolygon(4, secondQuad, !secondEdgeMatches);
 }
 
 } // namespace blink