Don't always force recalc for getComputedStyle in shadow trees.

We used to force clean style and layout tree getComputedStyle queries to
elements inside shadow trees. This was because the traversal in
Document::NeedsLayoutTreeUpdateForNode() skipped slots and shadow roots.
Now that slots are included in the flat tree, we can simply add checks
for shadow roots walking up the flat tree.

TEST=fast/dom/shadow/sibling-rules-under-shadow-root.html

Bug: 704421
Change-Id: Iee46f326ea96c0a4fad3e09b7784cf86d1dcdc85
Reviewed-on: https://chromium-review.googlesource.com/950042
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Hayato Ito <hayato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542386}

third_party/WebKit/Source/core/BUILD.gn

@@ -1674,6 +1674,7 @@ jumbo_source_set("unit_tests") {
     "css/ActiveStyleSheetsTest.cpp",
     "css/AffectedByPseudoTest.cpp",
     "css/CSSCalculationValueTest.cpp",
+    "css/CSSComputedStyleDeclarationTest.cpp",
     "css/CSSFontFaceSourceTest.cpp",
     "css/CSSGradientValueTest.cpp",
     "css/CSSPageRuleTest.cpp",

third_party/WebKit/Source/core/css/CSSComputedStyleDeclaration.cpp

@@ -361,10 +361,7 @@ const CSSValue* CSSComputedStyleDeclaration::GetPropertyCSSValue(
   LayoutObject* layout_object = StyledLayoutObject();
   const ComputedStyle* style = ComputeComputedStyle();
 
-  // TODO(futhark@chromium.org): IsInShadowTree() should not be necessary here.
-  // See http://crbug.com/704421
-  if (property_class.IsLayoutDependent(style, layout_object) ||
-      styled_node->IsInShadowTree()) {
+  if (property_class.IsLayoutDependent(style, layout_object)) {
     document.UpdateStyleAndLayoutIgnorePendingStylesheetsForNode(styled_node);
     styled_node = StyledNode();
     style = ComputeComputedStyle();

third_party/WebKit/Source/core/css/CSSComputedStyleDeclarationTest.cpp

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/css/CSSComputedStyleDeclaration.h"
+
+#include "core/dom/ShadowRoot.h"
+#include "core/html/HTMLElement.h"
+#include "core/testing/PageTestBase.h"
+
+namespace blink {
+
+class CSSComputedStyleDeclarationTest : public PageTestBase {};
+
+TEST_F(CSSComputedStyleDeclarationTest, CleanAncestorsNoRecalc) {
+  GetDocument().body()->SetInnerHTMLFromString(R"HTML(
+    <div id=dirty></div>
+    <div>
+      <div id=target style='color:green'></div>
+    </div>
+  )HTML");
+  GetDocument().View()->UpdateAllLifecyclePhases();
+  EXPECT_FALSE(GetDocument().NeedsLayoutTreeUpdate());
+
+  GetDocument().getElementById("dirty")->setAttribute("style", "color:pink");
+  EXPECT_TRUE(GetDocument().NeedsLayoutTreeUpdate());
+
+  Element* target = GetDocument().getElementById("target");
+  CSSComputedStyleDeclaration* computed =
+      CSSComputedStyleDeclaration::Create(target);
+
+  EXPECT_STREQ("rgb(0, 128, 0)",
+               computed->GetPropertyValue(CSSPropertyColor).Utf8().data());
+  EXPECT_TRUE(GetDocument().NeedsLayoutTreeUpdate());
+}
+
+TEST_F(CSSComputedStyleDeclarationTest, CleanShadowAncestorsNoRecalc) {
+  GetDocument().body()->SetInnerHTMLFromString(R"HTML(
+    <div id=dirty></div>
+    <div id=host></div>
+  )HTML");
+
+  Element* host = GetDocument().getElementById("host");
+
+  ShadowRoot& shadow_root =
+      host->AttachShadowRootInternal(ShadowRootType::kOpen);
+  shadow_root.SetInnerHTMLFromString(R"HTML(
+    <div id=target style='color:green'></div>
+  )HTML");
+
+  GetDocument().View()->UpdateAllLifecyclePhases();
+  EXPECT_FALSE(GetDocument().NeedsLayoutTreeUpdate());
+
+  GetDocument().getElementById("dirty")->setAttribute("style", "color:pink");
+  EXPECT_TRUE(GetDocument().NeedsLayoutTreeUpdate());
+
+  Element* target = shadow_root.getElementById("target");
+  CSSComputedStyleDeclaration* computed =
+      CSSComputedStyleDeclaration::Create(target);
+
+  EXPECT_STREQ("rgb(0, 128, 0)",
+               computed->GetPropertyValue(CSSPropertyColor).Utf8().data());
+  EXPECT_EQ(RuntimeEnabledFeatures::SlotInFlatTreeEnabled(),
+            GetDocument().NeedsLayoutTreeUpdate());
+}
+
+}  // namespace blink

third_party/WebKit/Source/core/dom/Document.cpp

@@ -2301,9 +2301,16 @@ bool Document::NeedsLayoutTreeUpdateForNode(const Node& node) const {
     return true;
   for (const ContainerNode* ancestor = LayoutTreeBuilderTraversal::Parent(node);
        ancestor; ancestor = LayoutTreeBuilderTraversal::Parent(*ancestor)) {
+    if (ShadowRoot* root = ancestor->GetShadowRoot()) {
+      if (root->NeedsStyleRecalc() || root->NeedsStyleInvalidation() ||
+          root->NeedsAdjacentStyleRecalc()) {
+        return true;
+      }
+    }
     if (ancestor->NeedsStyleRecalc() || ancestor->NeedsStyleInvalidation() ||
-        ancestor->NeedsAdjacentStyleRecalc())
+        ancestor->NeedsAdjacentStyleRecalc()) {
       return true;
+    }
   }
   return false;
 }