[Devtools] Fix hover issue with darktheme in network

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

 /**
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 642 matching lines @@
               entryIndex, context, text, barX, barY, barWidth, barHeight, unclippedBarX, this._timeToPixel))
         continue;
       if (!text || !text.length)
         continue;
       context.fillStyle = this._dataProvider.textColor(entryIndex);
       context.fillText(text, barX + textPadding, barY + textBaseHeight);
     }
 
     context.restore();
 
-    UI.TimelineGrid.drawCanvasGrid(context, this._calculator, 3);
+    const headerHeight = 15;
+    UI.TimelineGrid.drawCanvasGrid(context, this._calculator, 3, headerHeight);
     this._drawMarkers();
     this._drawGroupHeaders(width, height);
 
     this._updateElementPosition(this._highlightElement, this._highlightedEntryIndex);
     this._updateElementPosition(this._selectedElement, this._selectedEntryIndex);
     this._updateMarkerHighlight();
   }
 
   /**
    * @param {number} width
@@ skipping 817 matching lines @@
   }
 
   /**
    * @override
    * @return {number}
    */
   boundarySpan() {
     return this._maximumBoundaries - this._minimumBoundaries;
   }
 };