asWebviewUri  
  Convert a uri for the local file system to one that can be used inside webviews.
Webviews cannot directly load resources from the workspace or local file system using file: uris. The asWebviewUri function takes a local file: uri and converts it into a uri that can be used inside of a webview to load the same resource:
webview.html = `<img src="${webview.asWebviewUri(vscode.Uri.file('/Users/codey/workspace/cat.gif'))}">`Content copied to clipboard