DevTools: add support for polling for coverage data in CSS agent

third_party/WebKit/Source/core/css/resolver/StyleRuleUsageTracker.cpp

 // Copyright 2016 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/resolver/StyleRuleUsageTracker.h"
 
+#include "core/css/CSSStyleSheet.h"
 #include "core/css/StyleRule.h"
 
 namespace blink {
 
-bool StyleRuleUsageTracker::contains(StyleRule* rule) const {
-  return m_ruleList.contains(rule);
+StyleRuleUsageTracker::RuleListByStyleSheet StyleRuleUsageTracker::takeDelta() {
+  RuleListByStyleSheet result;
+  result.swap(m_usedRulesDelta);
+  return result;
+}
+
+void StyleRuleUsageTracker::track(const StyleRule* rule,
+                                  const CSSStyleSheet* parentSheet) {
+  if (!parentSheet)
+    return;
+  if (!m_usedRules.insert(rule).isNewEntry)

[pfeldman, 2017/03/21 18:04:16]

This is not entirely correct due to stylesheetcontents content-based dedupe.

+    return;
+  auto it = m_usedRulesDelta.find(parentSheet);
+  if (it != m_usedRulesDelta.end()) {
+    it->value.push_back(rule);
+  } else {
+    m_usedRulesDelta.insert(parentSheet, HeapVector<Member<const StyleRule>>())
+        .storedValue->value.push_back(rule);
+  }
 }
 
 DEFINE_TRACE(StyleRuleUsageTracker) {
-  visitor->trace(m_ruleList);
+  visitor->trace(m_usedRules);
+  visitor->trace(m_usedRulesDelta);
 }
 
 }  // namespace blink