[IO] Return correct non-empty value in slow path with effects.

Previously, we always returned true for "is mapped rect non-
empty?" from LocalToAncestorVisualRect in the presence of
effect nodes which may move pixels.

Now return true only if the actual computed rect is non-empty.

Bug:910741

TBR=chrishtr@chromium.org

(cherry picked from commit 5aeac68)

Change-Id: I41935060706b887f58ed14a179d8975bee02c39f
Reviewed-on: https://chromium-review.googlesource.com/c/1359692
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#613625}
Reviewed-on: https://chromium-review.googlesource.com/c/1363954
Cr-Commit-Position: refs/branch-heads/3626@{#85}
Cr-Branched-From: d897fb1-refs/heads/master@{#612437}

third_party/blink/renderer/platform/graphics/paint/geometry_mapper.cc

@@ -287,7 +287,7 @@ bool GeometryMapper::SlowLocalToAncestorVisualRectWithEffects(
 
   // Many effects (e.g. filters, clip-paths) can make a clip rect not tight.
   mapping_rect.ClearIsTight();
-  return true;
+  return !mapping_rect.Rect().IsEmpty();
 }
 
 FloatClipRect GeometryMapper::LocalToAncestorClipRect(

third_party/blink/renderer/platform/graphics/paint/geometry_mapper_test.cc

@@ -394,6 +394,21 @@ TEST_P(GeometryMapperTest, SimpleClipInclusiveIntersect) {
   EXPECT_CLIP_RECT_EQ(FloatClipRect(FloatRect()), actual_clip_rect);
 }
 
+TEST_P(GeometryMapperTest, SimpleClipPlusOpacity) {
+  auto clip = CreateClip(c0(), &t0(), FloatRoundedRect(10, 10, 50, 50));
+  local_state.SetClip(clip.get());
+
+  auto opacity = CreateOpacityEffect(e0(), 0.99);
+  local_state.SetEffect(opacity.get());
+
+  FloatClipRect actual_clip_rect(FloatRect(60, 10, 10, 10));
+  auto intersects = GeometryMapper::LocalToAncestorVisualRect(
+      local_state, ancestor_state, actual_clip_rect);
+
+  EXPECT_TRUE(actual_clip_rect.Rect().IsEmpty());
+  EXPECT_FALSE(intersects);
+}
+
 TEST_P(GeometryMapperTest, RoundedClip) {
   FloatRoundedRect rect(FloatRect(10, 10, 50, 50),
                         FloatRoundedRect::Radii(FloatSize(1, 1), FloatSize(),