Reland "Cache animation base computed style only on default StyleForElement()"

This reverts commit 0bc5ba70.

Reason for revert: Not the cause of crbug.com/996037.

Original change's description:
> Revert "Cache animation base computed style only on default StyleForElement()"
> 
> This reverts commit a1fe850a.
> 
> Reason for revert: speculative revert for crbug.com/996037.
> 
> Original change's description:
> > Cache animation base computed style only on default StyleForElement()
> > 
> > StyleForElement() can be used to get the default style (i.e. the
> > style that will be applied on the element), or style derived from
> > custom parent style for e.g. inherited first line style. We should
> > cache animation base computed style in the first case only.
> > 
> > Bug: 989490
> > Change-Id: Ia30b3e7bcd65cdb9456eb925e5c24f156353bff9
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1753030
> > Reviewed-by: Rune Lillesveen <futhark@chromium.org>
> > Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#686915}
> 
> TBR=wangxianzhu@chromium.org,futhark@chromium.org
> 
> # Not skipping CQ checks because original CL landed > 1 day ago.
> 
> Bug: 989490,996037
> Change-Id: Ib12e4e55e70eaeb2c82ca173c145c225c1d79802
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1763343
> Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
> Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#689165}

TBR=wangxianzhu@chromium.org,futhark@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 989490, 996037
Change-Id: I32dc5509075cfae90721dadc49144a309b40b901
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1776380Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#691678}

third_party/blink/renderer/core/css/resolver/style_resolver.cc

@@ -670,7 +670,7 @@ void StyleResolver::LoadPendingResources(StyleResolverState& state) {
   state.GetElementStyleResources().LoadPendingResources(state.Style());
 }
 
-static const ComputedStyle* CalculateBaseComputedStyle(
+static const ComputedStyle* CachedAnimationBaseComputedStyle(
     StyleResolverState& state) {
   if (!state.GetAnimatingElement())
     return nullptr;
@@ -691,7 +691,7 @@ static const ComputedStyle* CalculateBaseComputedStyle(
   return element_animations->BaseComputedStyle();
 }
 
-static void UpdateBaseComputedStyle(StyleResolverState& state) {
+static void UpdateAnimationBaseComputedStyle(StyleResolverState& state) {
   if (!state.GetAnimatingElement())
     return;
 
@@ -723,10 +723,19 @@ scoped_refptr<ComputedStyle> StyleResolver::StyleForElement(
   StyleResolverState state(GetDocument(), *element, default_parent,
                            default_layout_parent);
 
-  const ComputedStyle* base_computed_style = CalculateBaseComputedStyle(state);
-
-  if (base_computed_style) {
-    state.SetStyle(ComputedStyle::Clone(*base_computed_style));
+  // This function can return different results with different last 3 params,
+  // but we can only cache one base computed style for animations, thus we cache
+  // only when this function is called with default last 3 params.
+  bool can_cache_animation_base_computed_style =
+      !default_parent && !default_layout_parent &&
+      matching_behavior == kMatchAllRules;
+  const ComputedStyle* animation_base_computed_style =
+      can_cache_animation_base_computed_style
+          ? CachedAnimationBaseComputedStyle(state)
+          : nullptr;
+
+  if (animation_base_computed_style) {
+    state.SetStyle(ComputedStyle::Clone(*animation_base_computed_style));
     if (!state.ParentStyle()) {
       state.SetParentStyle(InitialStyleForElement(GetDocument()));
       state.SetLayoutParentStyle(state.ParentStyle());
@@ -770,7 +779,7 @@ scoped_refptr<ComputedStyle> StyleResolver::StyleForElement(
     state.Style()->SetInsideLink(link_state);
   }
 
-  if (!base_computed_style) {
+  if (!animation_base_computed_style) {
     GetDocument().GetStyleEngine().EnsureUAStyleForElement(*element);
 
     ElementRuleCollector collector(state.ElementContext(), selector_filter_,
@@ -821,7 +830,8 @@ scoped_refptr<ComputedStyle> StyleResolver::StyleForElement(
 
     StyleAdjuster::AdjustComputedStyle(state, element);
 
-    UpdateBaseComputedStyle(state);
+    if (can_cache_animation_base_computed_style)
+      UpdateAnimationBaseComputedStyle(state);
   } else {
     INCREMENT_STYLE_STATS_COUNTER(GetDocument().GetStyleEngine(),
                                   base_styles_used, 1);
@@ -891,10 +901,11 @@ bool StyleResolver::PseudoStyleForElementInternal(
 
   SelectorFilterParentScope::EnsureParentStackIsPushed();
 
-  const ComputedStyle* base_computed_style = CalculateBaseComputedStyle(state);
+  const ComputedStyle* animation_base_computed_style =
+      CachedAnimationBaseComputedStyle(state);
 
-  if (base_computed_style) {
-    state.SetStyle(ComputedStyle::Clone(*base_computed_style));
+  if (animation_base_computed_style) {
+    state.SetStyle(ComputedStyle::Clone(*animation_base_computed_style));
   } else if (pseudo_style_request.AllowsInheritance(state.ParentStyle())) {
     scoped_refptr<ComputedStyle> style = ComputedStyle::Create();
     style->InheritFrom(*state.ParentStyle());
@@ -909,7 +920,7 @@ bool StyleResolver::PseudoStyleForElementInternal(
   // Since we don't use pseudo-elements in any of our quirk/print
   // user agent rules, don't waste time walking those rules.
 
-  if (!base_computed_style) {
+  if (!animation_base_computed_style) {
     // Check UA, user and author rules.
     ElementRuleCollector collector(state.ElementContext(), selector_filter_,
                                    state.Style());
@@ -936,7 +947,7 @@ bool StyleResolver::PseudoStyleForElementInternal(
     // in the StyleAdjuster::AdjustComputedStyle code.
     StyleAdjuster::AdjustComputedStyle(state, nullptr);
 
-    UpdateBaseComputedStyle(state);
+    UpdateAnimationBaseComputedStyle(state);
   }
 
   // FIXME: The CSSWG wants to specify that the effects of animations are

third_party/blink/renderer/core/css/resolver/style_resolver_test.cc

@@ -5,6 +5,7 @@
 #include "third_party/blink/renderer/core/css/resolver/style_resolver.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
+#include "third_party/blink/renderer/core/animation/element_animations.h"
 #include "third_party/blink/renderer/core/css/style_engine.h"
 #include "third_party/blink/renderer/core/dom/document.h"
 #include "third_party/blink/renderer/core/dom/node_computed_style.h"
@@ -33,4 +34,45 @@ TEST_F(StyleResolverTest, StyleForTextInDisplayNone) {
       To<Text>(GetDocument().body()->firstChild())));
 }
 
+TEST_F(StyleResolverTest, AnimationBaseComputedStyle) {
+  GetDocument().documentElement()->SetInnerHTMLFromString(R"HTML(
+    <style>
+      html { font-size: 10px; }
+      body { font-size: 20px; }
+    </style>
+    <div id="div">Test</div>
+  )HTML");
+  UpdateAllLifecyclePhasesForTest();
+
+  Element* div = GetDocument().getElementById("div");
+  StyleResolver* resolver = GetStyleEngine().Resolver();
+  ASSERT_TRUE(resolver);
+  ElementAnimations& animations = div->EnsureElementAnimations();
+  animations.SetAnimationStyleChange(true);
+
+  ASSERT_TRUE(resolver->StyleForElement(div));
+  EXPECT_EQ(20, resolver->StyleForElement(div)->FontSize());
+#if DCHECK_IS_ON()
+  EXPECT_FALSE(animations.BaseComputedStyle());
+#else
+  ASSERT_TRUE(animations.BaseComputedStyle());
+  EXPECT_EQ(20, animations.BaseComputedStyle()->FontSize());
+#endif
+
+  // Getting style with customized parent style should not affect cached
+  // animation base computed style.
+  const ComputedStyle* parent_style =
+      GetDocument().documentElement()->GetComputedStyle();
+  EXPECT_EQ(
+      10,
+      resolver->StyleForElement(div, parent_style, parent_style)->FontSize());
+#if DCHECK_IS_ON()
+  EXPECT_FALSE(animations.BaseComputedStyle());
+#else
+  ASSERT_TRUE(animations.BaseComputedStyle());
+  EXPECT_EQ(20, animations.BaseComputedStyle()->FontSize());
+#endif
+  EXPECT_EQ(20, resolver->StyleForElement(div)->FontSize());
+}
+
 }  // namespace blink