[Blink] Correctly derive context when no property changed

There was a mistake in PaintPropertyTreeBuilder::UpdateClipPathClip()
to early exit when properties didn't change. However in that case we
still have to update the context for descendants to inherit. This CL
removed the early exit.

BUG=836127

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I38b229b86bd9c2106ac32bf54d520d39cb892e0c
Reviewed-on: https://chromium-review.googlesource.com/1038705Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Tien-Ren Chen <trchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555275}

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

@@ -1046,9 +1046,6 @@ void FragmentPaintPropertyTreeBuilder::UpdateCssClip() {
 
 void FragmentPaintPropertyTreeBuilder::UpdateClipPathClip(
     bool spv1_compositing_specific_pass) {
-  if (!NeedsPaintPropertyUpdate())
-    return;
-
   // In SPv1*, composited path-based clip-path applies to a mask paint chunk
   // instead of actual contents. We have to delay until mask clip node has been
   // created first so we can parent under it.
@@ -1058,16 +1055,18 @@ void FragmentPaintPropertyTreeBuilder::UpdateClipPathClip(
   if (is_spv1_composited != spv1_compositing_specific_pass)
     return;
 
-  if (!NeedsClipPathClip(object_)) {
-    OnClearClip(properties_->ClearClipPathClip());
-  } else {
-    ClipPaintPropertyNode::State state;
-    state.local_transform_space = context_.current.transform;
-    state.clip_rect =
-        FloatRoundedRect(FloatRect(*fragment_data_.ClipPathBoundingBox()));
-    state.clip_path = fragment_data_.ClipPathPath();
-    OnUpdateClip(properties_->UpdateClipPathClip(context_.current.clip,
-                                                 std::move(state)));
+  if (NeedsPaintPropertyUpdate()) {
+    if (!NeedsClipPathClip(object_)) {
+      OnClearClip(properties_->ClearClipPathClip());
+    } else {
+      ClipPaintPropertyNode::State state;
+      state.local_transform_space = context_.current.transform;
+      state.clip_rect =
+          FloatRoundedRect(FloatRect(*fragment_data_.ClipPathBoundingBox()));
+      state.clip_path = fragment_data_.ClipPathPath();
+      OnUpdateClip(properties_->UpdateClipPathClip(context_.current.clip,
+                                                   std::move(state)));
+    }
   }
 
   if (properties_->ClipPathClip() && !spv1_compositing_specific_pass) {

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

@@ -5501,4 +5501,25 @@ TEST_P(PaintPropertyTreeBuilderTest, ClipHitTestChangeDoesNotCauseFullRepaint) {
   EXPECT_FALSE(child_layer->NeedsRepaint());
 }
 
+TEST_P(PaintPropertyTreeBuilderTest, ClipPathInheritanceWithoutMutation) {
+  // This test verifies we properly included the path-based clip-path in
+  // context when the clipping element didn't need paint property update.
+  SetBodyInnerHTML(R"HTML(
+    <div style="clip-path:circle();">
+      <div id="child" style="position:relative; width:100px; height:100px; background:green;"></div>
+    </div>
+  )HTML");
+
+  auto* child = ToLayoutBox(GetLayoutObjectByElementId("child"));
+  const auto* old_clip_state =
+      child->FirstFragment().LocalBorderBoxProperties().Clip();
+
+  child->SetNeedsPaintPropertyUpdate();
+  GetDocument().View()->UpdateAllLifecyclePhases();
+
+  const auto* new_clip_state =
+      child->FirstFragment().LocalBorderBoxProperties().Clip();
+  EXPECT_EQ(old_clip_state, new_clip_state);
+}
+
 }  // namespace blink