Manifest - Sandbox

Warning: Starting in version 57, Chrome will no longer allow external web content (including embedded frames and scripts) inside sandboxed pages. Please use a webview instead.

Defines a collection of app or extension pages that are to be served in a sandboxed unique origin, and optionally a Content Security Policy to use with them. Being in a sandbox has two implications:

A sandboxed page will not have access to extension or app APIs, or direct access to non-sandboxed pages (it may communicate with them via postMessage()).
A sandboxed page is not subject to the Content Security Policy (CSP) used by the rest of the app or extension (it has its own separate CSP value). This means that, for example, it can use inline script and eval.

For example, here's how to specify that two extension pages are to be served in a sandbox with a custom CSP:
```
{
  ...
  "sandbox": {
    "pages": [
      "page1.html",
      "directory/page2.html"
    ]
    // content_security_policy is optional.
    "content_security_policy":
        "sandbox allow-scripts; script-src 'self'"
  ],
  ...
}
```
If not specified, the default content_security_policy value is sandbox allow-scripts allow-forms allow-popups allow-modals; script-src 'self' 'unsafe-inline' 'unsafe-eval'; child-src 'self';. You can specify your CSP value to restrict the sandbox even further, but it must have the sandbox directive and may not have the allow-same-origin token (see the HTML5 specification for possible sandbox tokens). Also, the CSP you specify may not allow loading external web content inside sandboxed pages.

Note that you only need to list pages that you expected to be loaded in windows or frames. Resources used by sandboxed pages (e.g. stylesheets or JavaScript source files) do not need to appear in the sandboxed_page list, they will use the sandbox of the page that embeds them.

"Using eval in Chrome Extensions. Safely." goes into more detail about implementing a sandboxing workflow that enables use of libraries that would otherwise have issues executing under extension's default Content Security Policy.

Sandboxed page may only be specified when using manifest_version 2 or above.