This thread is for client side implementation. For server side policy, please refer to b/73517231.
No support case: Visited to a customer's office

Summary: 
Customer provides a business card management system for enterprise customers.
They wants to use Chromebook for their temp contractors to input an information on business cards. Their temp contractors are working from home, so the customer wants to block file uploading to unknown sites (because 'file' might have clients' PII).
At the same time, temp contractors needs to upload an information on business cards (including business card's pictures) to a portal site.

## Use case ##
["What" are they looking for a solution to? You need to be specific. Please don't just propose a feature but explain
what problem the proposed feature is meant to solve. How would a user/admin make use of the feature? Focus on the action/process the they want to perform.]
They wants to restrict users to block a file uploading to unknown sites, but need to upload files to their portal site (e.g. 'xxxx.abc.com/xxxxxxx').

## Motivation ##
["Why" does the use case exist? It's important to make sure the motivation behind the FR is a real problem. Do they have business/legal/etc. reasons that motivate this feature request? Good motivations are indicative of things that might affect other customers.]
X00 Chromebook opportunity is blocked by this issue.
We introduced CB as 'secure' device, so the customer expects to have this feature.

## Existing workarounds ##
[Note any workarounds that are available in the product today.]
Using an url filtering service, but they're not using an url filtering service.
Url filtering is not perfect for blocking a file upload.