Replace HeapHashSet with HeapHashMap

This is part of an ongoing effort to simplify heap collections
and limit the types they can support (specifically, this CL
removes the only existing non-member usage of HeapHashSet).

Bug: 1047147
Change-Id: I2d408a5bbace633002c354c17b13d892e1938dec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2025427Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739239}

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

@@ -15,11 +15,22 @@ StyleRuleUsageTracker::RuleListByStyleSheet StyleRuleUsageTracker::TakeDelta() {
   return result;
 }
 
+bool StyleRuleUsageTracker::InsertToUsedRulesMap(
+    const CSSStyleSheet* parent_sheet,
+    const StyleRule* rule) {
+  HeapHashSet<Member<const StyleRule>>* set =
+      used_rules_
+          .insert(parent_sheet,
+                  MakeGarbageCollected<HeapHashSet<Member<const StyleRule>>>())
+          .stored_value->value;
+  return set->insert(rule).is_new_entry;
+}
+
 void StyleRuleUsageTracker::Track(const CSSStyleSheet* parent_sheet,
                                   const StyleRule* rule) {
   if (!parent_sheet)
     return;
-  if (!used_rules_.insert(std::make_pair(parent_sheet, rule)).is_new_entry)
+  if (!InsertToUsedRulesMap(parent_sheet, rule))
     return;
   auto it = used_rules_delta_.find(parent_sheet);
   if (it != used_rules_delta_.end()) {

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

@@ -22,7 +22,10 @@ class StyleRuleUsageTracker : public GarbageCollected<StyleRuleUsageTracker> {
   void Trace(blink::Visitor*);
 
  private:
-  HeapHashSet<std::pair<Member<const CSSStyleSheet>, Member<const StyleRule>>>
+  bool InsertToUsedRulesMap(const CSSStyleSheet*, const StyleRule*);
+
+  HeapHashMap<Member<const CSSStyleSheet>,
+              Member<HeapHashSet<Member<const StyleRule>>>>
       used_rules_;
   RuleListByStyleSheet used_rules_delta_;
 };