DevTools: introduce "Track CSS Usage" experiment

third_party/WebKit/Source/devtools/front_end/components_lazy/CoverageProfile.js

+// 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.
+
+WebInspector.CoverageProfile = class {
+  constructor() {
+    this._updateTimer = null;
+    this._locationPool = new WebInspector.LiveLocationPool();
+    this.reset();
+  }
+
+  /**
+   * @return {!WebInspector.CoverageProfile}
+   */
+  static instance() {
+    if (!WebInspector.CoverageProfile._instance)
+      WebInspector.CoverageProfile._instance = new WebInspector.CoverageProfile();
+
+    return WebInspector.CoverageProfile._instance;
+  }
+
+  /**
+   * @param {string} url
+   * @param {!WebInspector.TextRange} range
+   */
+  appendUnusedRule(url, range) {
+    if (!url)
+      return;
+
+    var fileInfo = this._files.get(url);
+    if (!fileInfo) {
+      fileInfo = new Set();
+      this._files.set(url, fileInfo);
+    }
+    fileInfo.add(range);
+    this._scheduleUpdate();
+  }
+
+  reset() {
+    /** @type {!Map<string, !Set<!WebInspector.TextRange>>} */
+    this._files = new Map();

[lushnikov, 2016/11/09 00:45:30]

this is not a collection of "files". Let's come up with a better name? E.g.
"coverageForURL"

+    this._scheduleUpdate();
+  }
+
+  _scheduleUpdate() {
+    if (this._updateTimer)
+      return;
+
+    this._updateTimer = setTimeout(() => {
+      this._updateTimer = null;
+      this._doUpdate();
+    }, 0);
+  }
+
+  /**
+   * @param {!WebInspector.Event} event
+   */
+  _uiSourceCodeChanged(event) {
+    WebInspector.workspace.uiSourceCodes().forEach(
+        uiSourceCode => uiSourceCode.removeAllLineDecorations(WebInspector.CoverageProfile.LineDecorator.type));
+  }
+
+  _doUpdate() {
+    this._locationPool.disposeAll();
+    WebInspector.workspace.uiSourceCodes().forEach(
+        uiSourceCode => uiSourceCode.removeAllLineDecorations(WebInspector.CoverageProfile.LineDecorator.type));

[lushnikov, 2016/11/09 00:45:30]

can we be smarter and avoid traversing the whole workspace?

+
+    WebInspector.workspace.uiSourceCodes().forEach(
+        uiSourceCode => uiSourceCode.addEventListener(
+                            WebInspector.UISourceCode.Events.WorkingCopyChanged, this._uiSourceCodeChanged, this));

[lushnikov, 2016/11/09 00:45:30]

The workignCopyChanged happens for every keypress in the editor. You don't want
to do anything
expensive here, e.g. traversing the whole workspace (it might contain thousands
of UISourceCodes...).

Why do you want to do this at all?

+
+    for (var fileInfo of this._files) {

[lushnikov, 2016/11/09 00:45:30]

let's iterate keys here - this way you'll avoid unnecessary typecasts

for (var url of this._coverageForURL.keysArray()) {
   ...
}

+      var url = /** @type {string} */ (fileInfo[0]);
+      var uiSourceCode = WebInspector.workspace.uiSourceCodeForURL(url);
+      if (!uiSourceCode)
+        continue;
+
+      var target =
+          WebInspector.NetworkProject.targetForUISourceCode(uiSourceCode) || WebInspector.targetManager.mainTarget();

[lushnikov, 2016/11/09 00:45:30]

why do you need mainTarget?

+      var debuggerModel = target ? WebInspector.DebuggerModel.fromTarget(target) : null;

[lushnikov, 2016/11/09 00:45:30]

since you're dealing with CSS, you should not talk to DebuggerModel. @see
CSSModel

+      if (!debuggerModel)
+        continue;
+
+      for (var range of fileInfo[1]) {
+        for (var line  = range.startLine; line <= range.endLine; ++line) {
+
+          var rawLocation = debuggerModel.createRawLocationByURL(url, line, 0);

[lushnikov, 2016/11/09 00:45:31]

this whole code will not work; let's add a test which would catch this

+          if (rawLocation)
+            new WebInspector.CoverageProfile.Presentation(rawLocation, this._locationPool);
+          else if (uiSourceCode)
+            uiSourceCode.addLineDecoration(line, WebInspector.CoverageProfile.LineDecorator.type, 0);
+        }
+      }
+    }
+  }
+};
+
+WebInspector.CoverageProfile.Presentation = class {

[lushnikov, 2016/11/09 00:45:30]

probably you don't need this - unless it comes handy with SourceMaps

+  /**
+   * @param {!WebInspector.DebuggerModel.Location} rawLocation
+   * @param {!WebInspector.LiveLocationPool} locationPool
+   */
+  constructor(rawLocation, locationPool) {
+    WebInspector.debuggerWorkspaceBinding.createLiveLocation(rawLocation, this.updateLocation.bind(this), locationPool);

[lushnikov, 2016/11/09 00:45:30]

Debugger has nothing to do with styles; use cssWorkspaceBinding if you need to.

+    this._uiLocation = null;
+  }
+
+  /**
+   * @param {!WebInspector.LiveLocation} liveLocation
+   */
+  updateLocation(liveLocation) {
+    if (this._uiLocation)
+      this._uiLocation.uiSourceCode.removeLineDecoration(
+          this._uiLocation.lineNumber, WebInspector.CoverageProfile.LineDecorator.type);
+
+    this._uiLocation = liveLocation.uiLocation();
+    if (this._uiLocation)
+      this._uiLocation.uiSourceCode.addLineDecoration(
+          this._uiLocation.lineNumber, WebInspector.CoverageProfile.LineDecorator.type, 0);
+  }
+};
+
+/**
+ * @implements {WebInspector.UISourceCodeFrame.LineDecorator}
+ */
+WebInspector.CoverageProfile.LineDecorator = class {
+  /**
+   * @override
+   * @param {!WebInspector.UISourceCode} uiSourceCode
+   * @param {!WebInspector.CodeMirrorTextEditor} textEditor
+   */
+  decorate(uiSourceCode, textEditor) {
+    var gutterType = 'CodeMirror-gutter-coverage';
+
+    var decorations = uiSourceCode.lineDecorations(WebInspector.CoverageProfile.LineDecorator.type);
+    textEditor.uninstallGutter(gutterType);
+    if (!decorations)
+      return;
+
+    textEditor.installGutter(gutterType, false);
+
+    for (var decoration of decorations.values()) {
+      var element = createElementWithClass('div', 'text-editor-line-marker-coverage');
+      textEditor.setGutterDecoration(decoration.line(), gutterType, element);
+    }
+  }
+};
+
+WebInspector.CoverageProfile.LineDecorator.type = 'coverage';