src/vs/base/browser/ui/scrollbar/abstractScrollbar.ts/AbstractScrollbar/_sliderMouseDown
class AbstractScrollbar:	private _sliderMouseDown(e: IMouseEvent, onDragFinished: () => void): void {
		const initialMousePosition = this._sliderMousePosition(e);
		const initialMouseOrthogonalPosition = this._sliderOrthogonalMousePosition(e);
		const initialScrollbarState = this._scrollbarState.clone();
		this.slider.toggleClassName('active', true);

		this._mouseMoveMonitor.startMonitoring(
			e.target,
			e.buttons,
			standardMouseMoveMerger,
			(mouseMoveData: IStandardMouseMoveEventData) => {
				const mouseOrthogonalPosition = this._sliderOrthogonalMousePosition(mouseMoveData);
				const mouseOrthogonalDelta = Math.abs(mouseOrthogonalPosition - initialMouseOrthogonalPosition);

				if (platform.isWindows && mouseOrthogonalDelta > MOUSE_DRAG_RESET_DISTANCE) {
					// The mouse has wondered away from the scrollbar => reset dragging
					this._setDesiredScrollPositionNow(initialScrollbarState.getScrollPosition());
					return;
				}

				const mousePosition = this._sliderMousePosition(mouseMoveData);
				const mouseDelta = mousePosition - initialMousePosition;
				this._setDesiredScrollPositionNow(initialScrollbarState.getDesiredScrollPositionFromDelta(mouseDelta));
			},
			() => {
				this.slider.toggleClassName('active', false);
				this._host.onDragEnd();
				onDragFinished();
			}
		);

		this._host.onDragStart();
	}