DevTools: Make sure network and main flamechart scales are in sync.

third_party/WebKit/Source/devtools/front_end/ui_lazy/ChartViewport.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.
 /**
  * @unrestricted
  */
 UI.ChartViewport = class extends UI.VBox {
   constructor() {
     super(true);
 
     this.viewportElement = this.contentElement.createChild('div', 'fill');
     this.viewportElement.addEventListener('mousewheel', this._onMouseWheel.bind(this), false);
     this.viewportElement.addEventListener('keydown', this._handleZoomPanKeys.bind(this), false);
 
     UI.installInertialDragHandle(
         this.viewportElement, this._startDragging.bind(this), this._dragging.bind(this), this._endDragging.bind(this),
         '-webkit-grabbing', null);
     UI.installDragHandle(
         this.viewportElement, this._startRangeSelection.bind(this), this._rangeSelectionDragging.bind(this),
         this._endRangeSelection.bind(this), 'text', null);
 
+    this._alwaysShowVerticalScroll = false;
     this._vScrollElement = this.contentElement.createChild('div', 'flame-chart-v-scroll');
     this._vScrollContent = this._vScrollElement.createChild('div');
     this._vScrollElement.addEventListener('scroll', this._onScroll.bind(this), false);
 
     this._selectionOverlay = this.contentElement.createChild('div', 'flame-chart-selection-overlay hidden');
     this._selectedTimeSpanLabel = this._selectionOverlay.createChild('div', 'time-span');
 
     this.reset();
   }
 
+  alwaysShowVerticalScroll() {
+    this._alwaysShowVerticalScroll = true;
+    this._vScrollElement.classList.add('always-show-scrollbar');
+  }
+
   /**
    * @return {boolean}
    */
   isDragging() {
     return this._isDragging;
   }
 
   /**
    * @override
    * @return {!Array<!Element>}
    */
   elementsToRestoreScrollPositionsFor() {
     return [this._vScrollElement];
   }
 
   /**
    * @private
    */
   _updateScrollBar() {
-    var showScroll = this._totalHeight > this._offsetHeight;
+    const showScroll = this._alwaysShowVerticalScroll || this._totalHeight > this._offsetHeight;
     if (this._vScrollElement.classList.contains('hidden') !== showScroll)
       return;
     this._vScrollElement.classList.toggle('hidden', !showScroll);
     this._updateContentElementSize();
   }
 
   /**
    * @override
    */
   onResize() {
@@ skipping 368 matching lines @@
     }
     this._cancelAnimation();
     this._cancelWindowTimesAnimation = UI.animateFunction(
         this.element.window(), this._animateWindowTimes.bind(this),
         [{from: this._timeWindowLeft, to: startTime}, {from: this._timeWindowRight, to: endTime}], 5,
         this._animationCompleted.bind(this));
     this._pendingAnimationTimeLeft = startTime;
     this._pendingAnimationTimeRight = endTime;
   }
 };