Use StyleForLayoutObject for option to update stacking context properly.

We used OriginalStyleForLayoutObject which doesn't update animations or
stacking context. Hopefully a better fix for 813348.

Bug: 813348, 813439, 813836
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I93584261a935c4813f618a9291d384a5b1203ec7
Reviewed-on: https://chromium-review.googlesource.com/924705Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539093}

third_party/WebKit/Source/core/html/forms/HTMLOptionElement.cpp

@@ -91,7 +91,7 @@ void HTMLOptionElement::AttachLayoutTree(AttachContext& context) {
   if (!GetNonAttachedStyle() && ParentComputedStyle()) {
     if (HTMLSelectElement* select = OwnerSelectElement())
       select->UpdateListOnLayoutObject();
-    SetNonAttachedStyle(OriginalStyleForLayoutObject());
+    SetNonAttachedStyle(StyleForLayoutObject());
   }
   HTMLElement::AttachLayoutTree(option_context);
 }

third_party/WebKit/Source/core/layout/LayoutBoxModelObjectTest.cpp

@@ -1088,4 +1088,27 @@ TEST_F(LayoutBoxModelObjectTest, BackfaceVisibilityChange) {
   EXPECT_FALSE(target_layer->NeedsRepaint());
 }
 
+TEST_F(LayoutBoxModelObjectTest, UpdateStackingContextForOption) {
+  SetBodyInnerHTML(R"HTML(
+    <style>
+      @keyframes op {
+        0% { opacity: 0 }
+        100% { opacity: 1 }
+      }
+      option {
+        animation: op 0.001s;
+      }
+    </style>
+    <select multiple size=1>
+      <option id=opt>PASS</option>
+    </select>
+  )HTML");
+
+  auto* option_element = GetDocument().getElementById("opt");
+  auto* option_layout = option_element->GetLayoutObject();
+  ASSERT_TRUE(option_layout);
+  EXPECT_TRUE(option_layout->StyleRef().IsStackingContext());
+  EXPECT_TRUE(option_layout->StyleRef().HasCurrentOpacityAnimation());
+}
+
 }  // namespace blink

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp

@@ -663,11 +663,6 @@ static bool NeedsEffect(const LayoutObject& object) {
   const bool is_css_isolated_group =
       object.IsBoxModelObject() && style.IsStackingContext();
 
-  // TODO(chrishtr): this should not be necessary, since masks induce
-  // stacking contexts. See crbug.com/813348
-  if (style.HasMask())
-    return true;
-
   if (!is_css_isolated_group && !object.IsSVGChild())
     return false;