Correct the squashing origin w.r.t. the transformed ancestor to take into...

Correct the squashing origin w.r.t. the transformed ancestor to take into account rounding to integer
offsets.

Review URL: https://codereview.chromium.org/345613004

git-svn-id: svn://svn.chromium.org/blink/trunk@176457 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/LayoutTests/compositing/squashing/squash-transform-repainting-transformed-child-expected.txt

@@ -50,8 +50,8 @@ CASE 2, hovering over the outer div
               (bounds 276.00 276.00)
               (drawsContent 1)
               (repaint rects
-                (rect 0.00 0.00 131.00 131.00)
-                (rect 0.00 0.00 131.00 131.00)
+                (rect 0.00 0.00 132.00 132.00)
+                (rect 0.00 0.00 132.00 132.00)
               )
             )
           )
@@ -83,10 +83,10 @@ CASE 3, hovering over the inner div
               (bounds 276.00 276.00)
               (drawsContent 1)
               (repaint rects
-                (rect 17.00 20.00 87.00 87.00)
-                (rect 17.00 20.00 87.00 87.00)
-                (rect 0.00 0.00 131.00 131.00)
-                (rect 0.00 0.00 131.00 131.00)
+                (rect 18.00 21.00 87.00 87.00)
+                (rect 18.00 21.00 87.00 87.00)
+                (rect 0.00 0.00 132.00 132.00)
+                (rect 0.00 0.00 132.00 132.00)
               )
             )
           )

third_party/WebKit/Source/core/rendering/compositing/CompositedLayerMapping.cpp

@@ -551,9 +551,6 @@ void CompositedLayerMapping::updateSquashingLayerGeometry(const LayoutPoint& off
         totalSquashBounds.unite(squashedBounds);
     }
 
-    *offsetFromTransformedAncestor = referenceOffsetFromTransformedAncestor;
-    offsetFromTransformedAncestor->moveBy(totalSquashBounds.location());
-
     // The totalSquashBounds is positioned with respect to referenceLayer of this CompositedLayerMapping.
     // But the squashingLayer needs to be positioned with respect to the ancestor CompositedLayerMapping.
     // The conversion between referenceLayer and the ancestor CLM is already computed as
@@ -566,6 +563,9 @@ void CompositedLayerMapping::updateSquashingLayerGeometry(const LayoutPoint& off
     squashingLayer->setPosition(squashLayerBounds.location());
     squashingLayer->setSize(squashLayerBounds.size());
 
+    *offsetFromTransformedAncestor = referenceOffsetFromTransformedAncestor;
+    offsetFromTransformedAncestor->move(squashLayerOriginInOwningLayerSpace);
+
     // Now that the squashing bounds are known, we can convert the RenderLayer painting offsets
     // from CLM owning layer space to the squashing layer space.
     //