Fixing overlap checking for layers with pixel-moving backdrop-filters

Previous to this CL, overlap checking was incorrect for layers
that had a pixel-moving backdrop-filter applied. The WPT test
external/wpt/css/filter-effects/backdrop-filter-paint-order.html
was the best indicator of this bug - a backdrop-filter painted
*after* adjoining but not overlapping content would be improperly
merged, and blurred content would be observed. This is now fixed.

Bug: 622128
Change-Id: I07539f5fbdc9c6e9cfaf6d4116b8de3dd62d1e94
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1607101
Commit-Queue: Philip Rogers <pdr@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Auto-Submit: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659494}

third_party/blink/renderer/core/paint/paint_layer.cc

@@ -2615,10 +2615,18 @@ LayoutRect PaintLayer::BoundingBoxForCompositingOverlapTest() const {
   // TODO(trchen): Layer fragmentation is inhibited across compositing boundary.
   // Should we return the unfragmented bounds for overlap testing? Or perhaps
   // assume fragmented layers always overlap?
-  return OverlapBoundsIncludeChildren()
-             ? BoundingBoxForCompositingInternal(
-                   *this, nullptr, kNeverIncludeTransformForAncestorLayer)
-             : FragmentsBoundingBox(this);
+  LayoutRect bounding_box =
+      OverlapBoundsIncludeChildren()
+          ? BoundingBoxForCompositingInternal(
+                *this, nullptr, kNeverIncludeTransformForAncestorLayer)
+          : FragmentsBoundingBox(this);
+  const ComputedStyle& style = GetLayoutObject().StyleRef();
+  if (style.HasBackdropFilter() &&
+      style.BackdropFilter().HasFilterThatMovesPixels()) {
+    bounding_box = EnclosingLayoutRect(
+        style.BackdropFilter().MapRect(FloatRect(bounding_box)));
+  }
+  return bounding_box;
 }
 
 bool PaintLayer::OverlapBoundsIncludeChildren() const {

third_party/blink/web_tests/TestExpectations

@@ -1617,7 +1617,6 @@ crbug.com/538697 [ Win ] printing/webgl-oversized-printing.html [ Failure Crash
 crbug.com/497522 css3/filters/backdrop-filter-boundary.html [ Failure ]
 crbug.com/497522 css3/filters/backdrop-filter-bleeding.html [ Failure ]
 crbug.com/497522 css3/filters/backdrop-filter-svg.html [ Failure ]
-crbug.com/497522 external/wpt/css/filter-effects/backdrop-filter-paint-order.html [ Failure ]
 # ====== Backdrop-filter related tests END ======