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

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

Index: third_party/WebKit/Source/core/css/resolver/StyleRuleUsageTracker.cpp
diff --git a/third_party/WebKit/Source/core/css/resolver/StyleRuleUsageTracker.cpp b/third_party/WebKit/Source/core/css/resolver/StyleRuleUsageTracker.cpp
index bd4629c7ef482abcc9e223f9c795eafeee195499..3cb6529e90b6c3a437305abd2774c9361bdb57e9 100644
--- a/third_party/WebKit/Source/core/css/resolver/StyleRuleUsageTracker.cpp
+++ b/third_party/WebKit/Source/core/css/resolver/StyleRuleUsageTracker.cpp
@@ -8,12 +8,15 @@
 
 namespace blink {
 
-bool StyleRuleUsageTracker::contains(StyleRule* rule) const {
-  return m_ruleList.contains(rule);
+HeapVector<Member<StyleRule>> StyleRuleUsageTracker::takeDelta() {
+  HeapVector<Member<StyleRule>> result;
+  result.swap(m_ruleListDelta);
+  return result;
 }
 
 DEFINE_TRACE(StyleRuleUsageTracker) {
   visitor->trace(m_ruleList);
+  visitor->trace(m_ruleListDelta);
 }
 
 }  // namespace blink