DevTools: Fix mouse wheel when mouse is on the scrolled of the flamechart.

third_party/WebKit/Source/devtools/front_end/ui_lazy/ChartViewport.js

Index: third_party/WebKit/Source/devtools/front_end/ui_lazy/ChartViewport.js
diff --git a/third_party/WebKit/Source/devtools/front_end/ui_lazy/ChartViewport.js b/third_party/WebKit/Source/devtools/front_end/ui_lazy/ChartViewport.js
index 84ffa29873af63df5dd6c6032c44ffbd20719bb0..f8ac02df6ad8357a28c8f9d2e7ed7ad2527662dc 100644
--- a/third_party/WebKit/Source/devtools/front_end/ui_lazy/ChartViewport.js
+++ b/third_party/WebKit/Source/devtools/front_end/ui_lazy/ChartViewport.js
@@ -8,10 +8,10 @@ UI.ChartViewport = class extends UI.VBox {
   constructor() {
     super(true);
 
-    this.contentElement.addEventListener('mousewheel', this._onMouseWheel.bind(this), false);
-    this.contentElement.addEventListener('keydown', this._handleZoomPanKeys.bind(this), false);
-
     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);