DevTools: Disable timeline network pane resizer when network group is collapsed.

third_party/WebKit/Source/devtools/front_end/timeline/TimelineNetworkFlameChart.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.
 
 /**
  * @implements {PerfUI.FlameChartDataProvider}
  * @unrestricted
  */
 Timeline.TimelineFlameChartNetworkDataProvider = class {
   /**
@@ skipping 349 matching lines @@
   }
 
   /**
    * @return {number}
    */
   preferredHeight() {
     return this._style.height * (this._group.expanded ? Number.constrain(this._maxLevel + 1, 4, 8.5) : 1);
   }
 
   /**
+   * @return {boolean}
+   */
+  isExpanded() {
+    return this._group.expanded;
+  }
+
+  /**
    * @override
    * @param {number} value
    * @param {number=} precision
    * @return {string}
    */
   formatValue(value, precision) {
     return Number.preciseMillisToString(value, precision);
   }
 
   /**
    * @override
    * @param {number} entryIndex
    * @return {boolean}
    */
   canJumpToEntry(entryIndex) {
     return false;
   }
 };