Don't create CSSAnimationData to apply initial values.

ComputedStyle::Animations() are null if all values are initial. If we
apply initial we don't need to create the object.

The same applies to CSSTransitionData.

Change-Id: I4c529a9df1764ba04560554892a46c452734d26a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2489621Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819540}

third_party/blink/renderer/build/scripts/core/css/properties/templates/style_builder_functions.tmpl

@@ -218,6 +218,8 @@ To<Longhand>(resolved_property).{{apply_call}};
     {% set animation = 'Animation' if property.style_builder_template == 'animation' else 'Transition' %}
     {% set vector = attribute + "List()" %}
     {% call(property) apply_initial(property) %}
+  if (!state.Style()->{{animation}}s())
+    return;
   CSS{{animation}}Data& data = state.Style()->Access{{animation}}s();
   data.{{vector}}.clear();
   data.{{vector}}.push_back(CSS{{animation}}Data::Initial{{attribute}}());

third_party/blink/renderer/core/style/computed_style_test.cc

@@ -1096,4 +1096,24 @@ TEST(ComputedStyleTest, ClonedStyleTransitionsAreIndependent) {
   EXPECT_EQ(1u, style->Transitions()->PropertyList().size());
 }
 
+TEST(ComputedStyleTest, ApplyInitialAnimationNameAndTransitionProperty) {
+  std::unique_ptr<DummyPageHolder> dummy_page_holder_ =
+      std::make_unique<DummyPageHolder>(IntSize(0, 0), nullptr);
+
+  const ComputedStyle* initial = &ComputedStyle::InitialStyle();
+  StyleResolverState state(dummy_page_holder_->GetDocument(),
+                           *dummy_page_holder_->GetDocument().documentElement(),
+                           initial, initial);
+
+  scoped_refptr<ComputedStyle> style = ComputedStyle::Create();
+  state.SetStyle(style);
+  EXPECT_FALSE(style->Animations());
+  EXPECT_FALSE(style->Transitions());
+
+  To<Longhand>(GetCSSPropertyAnimationName()).ApplyInitial(state);
+  To<Longhand>(GetCSSPropertyTransitionProperty()).ApplyInitial(state);
+  EXPECT_FALSE(style->Animations());
+  EXPECT_FALSE(style->Transitions());
+}
+
 }  // namespace blink