[mpc] Clear CachedMatchedProperties::matched_properties_types

Not really part of the MatchedPropertiesCache project, but we are
obviously missing a clear() call for the matched_properties_types
vector. It looks to me like this could potentially cause non-
deterministic crashes in case of hash collisions (operator== makes
assumptions about the size this vector), although no such crashes are
known.

Bug: 1057072
Change-Id: Ia741544fe2e69eba505c57e8315e01786674a56f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2207153
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#770371}

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

@@ -69,6 +69,7 @@ void CachedMatchedProperties::Set(
 
 void CachedMatchedProperties::Clear() {
   matched_properties.clear();
+  matched_properties_types.clear();
   computed_style = nullptr;
   parent_computed_style = nullptr;
   dependencies.clear();

third_party/blink/renderer/core/css/resolver/matched_properties_cache.h

@@ -36,7 +36,7 @@ namespace blink {
 class ComputedStyle;
 class StyleResolverState;
 
-class CachedMatchedProperties final
+class CORE_EXPORT CachedMatchedProperties final
     : public GarbageCollected<CachedMatchedProperties> {
  public:
   // Caches data of MatchedProperties. See |MatchedPropertiesCache::Cache| for

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

@@ -92,6 +92,35 @@ class MatchedPropertiesCacheTest : public PageTestBase,
   }
 };
 
+TEST_F(MatchedPropertiesCacheTest, ClearEntry) {
+  MatchResult result;
+  result.AddMatchedProperties(
+      css_test_helpers::ParseDeclarationBlock("top:inherit"));
+
+  auto style = CreateStyle();
+  auto parent = CreateStyle();
+
+  HashSet<CSSPropertyName> dependencies;
+  dependencies.insert(CSSPropertyName(CSSPropertyID::kTop));
+
+  auto* entry = MakeGarbageCollected<CachedMatchedProperties>();
+  entry->Set(*style, *parent, result.GetMatchedProperties(), dependencies);
+
+  EXPECT_TRUE(entry->computed_style);
+  EXPECT_TRUE(entry->parent_computed_style);
+  EXPECT_FALSE(entry->matched_properties.IsEmpty());
+  EXPECT_FALSE(entry->matched_properties_types.IsEmpty());
+  EXPECT_FALSE(entry->dependencies.IsEmpty());
+
+  entry->Clear();
+
+  EXPECT_FALSE(entry->computed_style);
+  EXPECT_FALSE(entry->parent_computed_style);
+  EXPECT_TRUE(entry->matched_properties.IsEmpty());
+  EXPECT_TRUE(entry->matched_properties_types.IsEmpty());
+  EXPECT_TRUE(entry->dependencies.IsEmpty());
+}
+
 TEST_F(MatchedPropertiesCacheTest, AllowedKeyValues) {
   unsigned empty = HashTraits<unsigned>::EmptyValue();
   unsigned deleted = std::numeric_limits<unsigned>::max();