dom snapshot iframe placeholder HTML not rendering

[kuceb]

• when viewing dom snapshot, I should see placeholder HTML inside iframe
  problem:
• something about how inlined data: html changed and cannot handle the # in color: #888

expected:

actual:

found in:
Cypress 3.4.1 (since unknown)
browsers: chromium 74 on linux

proposed solution:

switch to base64 encoding and use btoa(contents) to encode our html

[cypress-bot]

The code for this is done in cypress-io/cypress#5296, but has yet to be released.
We'll update this issue and reference the changelog when it's released.