Out of a spritesheet (if you have a separately saved icon already go to 2.):
largeIcons.svg in Inkscape.src/ version of the spritesheet._icon.svg suffix. For instance list_icon.svg.Add respective entries to .gni files.
devtols_image_files list in devtools_image_files.gni.grd_files_release_sources list in devtools_grd_files.gni.Optimize:
./scripts/optimize_svg_images.py.Images/list_icon.svg from Images/src/list_icon.svg by rounding numbers and removing hopefully unnecessary content. However, it might end up distorting/destroying the icon, especially if it is too small. Make sure to open the output of the optimiztion process (e.g. Images/list_icon.svg) in Inkscape and inspect it for damage. Enlarging the input image, as desribed in step (1) usually circumvents this.Use Icon component in the DevTools front-end: