Use WeakMember for CSSStyleSheet's adopted tree scopes

Currently we use strong references which will keep the shadow roots
from getting garbage collected.

Bug: 1002763
Change-Id: I62da84e94eaf52504efc80f1468349ee6d2f4fdc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1798222Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Rakina Zata Amni <rakina@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695953}

third_party/blink/renderer/core/css/css_style_sheet.h

@@ -215,6 +215,9 @@ class CORE_EXPORT CSSStyleSheet final : public StyleSheet {
 
   void SetLoadCompleted(bool);
 
+  FRIEND_TEST_ALL_PREFIXES(
+      CSSStyleSheetTest,
+      GarbageCollectedShadowRootsRemovedFromAdoptedTreeScopes);
   FRIEND_TEST_ALL_PREFIXES(CSSStyleSheetTest,
                            CSSStyleSheetConstructionWithEmptyCSSStyleSheetInit);
   FRIEND_TEST_ALL_PREFIXES(
@@ -252,7 +255,7 @@ class CORE_EXPORT CSSStyleSheet final : public StyleSheet {
 
   Member<Node> owner_node_;
   Member<CSSRule> owner_rule_;
-  HeapHashSet<Member<TreeScope>> adopted_tree_scopes_;
+  HeapHashSet<WeakMember<TreeScope>> adopted_tree_scopes_;
   Member<Document> associated_document_;
   HashSet<AtomicString> custom_element_tag_names_;
   Member<ScriptPromiseResolver> resolver_;

third_party/blink/renderer/core/css/css_style_sheet_test.cc

@@ -4,6 +4,7 @@
 
 #include "third_party/blink/renderer/core/css/css_style_sheet.h"
 #include "testing/gtest/include/gtest/gtest.h"
+#include "third_party/blink/public/web/web_heap.h"
 #include "third_party/blink/renderer/bindings/core/v8/media_list_or_string.h"
 #include "third_party/blink/renderer/bindings/core/v8/script_function.h"
 #include "third_party/blink/renderer/bindings/core/v8/script_promise.h"
@@ -13,6 +14,7 @@
 #include "third_party/blink/renderer/core/css/css_rule_list.h"
 #include "third_party/blink/renderer/core/css/css_style_sheet_init.h"
 #include "third_party/blink/renderer/core/css/media_list.h"
+#include "third_party/blink/renderer/core/dom/shadow_root.h"
 #include "third_party/blink/renderer/core/testing/page_test_base.h"
 
 namespace blink {
@@ -70,4 +72,31 @@ TEST_F(CSSStyleSheetTest,
   ASSERT_FALSE(exception_state.HadException());
 }
 
+TEST_F(CSSStyleSheetTest,
+       GarbageCollectedShadowRootsRemovedFromAdoptedTreeScopes) {
+  SetBodyInnerHTML("<div id='host_a'></div><div id='host_b'></div>");
+  auto* host_a = GetElementById("host_a");
+  auto& shadow_a = host_a->AttachShadowRootInternal(ShadowRootType::kOpen);
+  auto* host_b = GetElementById("host_b");
+  auto& shadow_b = host_b->AttachShadowRootInternal(ShadowRootType::kOpen);
+  DummyExceptionStateForTesting exception_state;
+  CSSStyleSheetInit* init = CSSStyleSheetInit::Create();
+  CSSStyleSheet* sheet =
+      CSSStyleSheet::Create(GetDocument(), init, exception_state);
+
+  HeapVector<Member<CSSStyleSheet>> adopted_sheets;
+  adopted_sheets.push_back(sheet);
+  shadow_a.SetAdoptedStyleSheets(adopted_sheets);
+  shadow_b.SetAdoptedStyleSheets(adopted_sheets);
+
+  EXPECT_EQ(sheet->adopted_tree_scopes_.size(), 2u);
+  EXPECT_EQ(shadow_a.AdoptedStyleSheets().size(), 1u);
+  EXPECT_EQ(shadow_b.AdoptedStyleSheets().size(), 1u);
+
+  host_a->remove();
+  WebHeap::CollectAllGarbageForTesting();
+  EXPECT_EQ(sheet->adopted_tree_scopes_.size(), 1u);
+  EXPECT_EQ(shadow_b.AdoptedStyleSheets().size(), 1u);
+}
+
 }  // namespace blink