Backend for css rule tracking

third_party/WebKit/Source/devtools/front_end/sdk/CSSModel.js

Index: third_party/WebKit/Source/devtools/front_end/sdk/CSSModel.js
diff --git a/third_party/WebKit/Source/devtools/front_end/sdk/CSSModel.js b/third_party/WebKit/Source/devtools/front_end/sdk/CSSModel.js
index c821e3832fb5f9e934e6198b5399c755bb7c01a8..5eb9c09962f42674140a292252557348b572b26f 100644
--- a/third_party/WebKit/Source/devtools/front_end/sdk/CSSModel.js
+++ b/third_party/WebKit/Source/devtools/front_end/sdk/CSSModel.js
@@ -439,6 +439,29 @@ WebInspector.CSSModel = class extends WebInspector.SDKModel {
         .catchException(false);
   }
 
+  startRuleUsageTracking() {
+    this._agent.startRuleUsageTracking();
+  }
+
+  /**
+   * @return {!Promise<?Array<!WebInspector.CSSModel.RuleUsageTracker>>}
+   */
+  ruleListPromise() {
+    /**
+     * @param {?string} error
+     * @param {!Array<!CSSAgent.RuleUsage>=} ruleUsage
+     * @return {?Array<!WebInspector.CSSModel.RuleUsageTracker>}
+     */
+    function usedRulesCallback(error, ruleUsage) {
+      if (error || !ruleUsage)
+        return null;
+
+      return ruleUsage.map(rule => ({range: rule.range, styleSheetId: rule.styleSheetId, wasUsed: rule.used}));
+    }
+
+    return this._agent.stopRuleUsageTracking(usedRulesCallback);
+  }
+
   /**
    * @return {!Promise.<!Array.<!WebInspector.CSSMedia>>}
    */
@@ -990,6 +1013,9 @@ WebInspector.CSSModel = class extends WebInspector.SDKModel {
   }
 };
 
+/** @typedef {!{range: !CSSAgent.SourceRange, styleSheetId: !CSSAgent.StyleSheetId, wasUsed: boolean}} */
+WebInspector.CSSModel.RuleUsageTracker;

[caseq, 2016/11/03 00:13:08]

Why is it called tracker? Is it tracking something? Let's call it just
WebInspector.CSSModel.RuleUsage

+
 /** @enum {symbol} */
 WebInspector.CSSModel.Events = {
   LayoutEditorChange: Symbol('LayoutEditorChange'),