src/vs/workbench/contrib/webview/browser/webviewElement.ts/WebviewElement/handleFocusChange
class WebviewElement:	protected handleFocusChange(isFocused: boolean): void {
		this._focused = isFocused;
		if (isFocused) {
			this._onDidFocus.fire();
		} else {
			this._onDidBlur.fire();
		}
	}