Waits until after at least one paint (double rAF). Use sparingly — e.g. once
before a long sync stretch so a loading overlay can appear. Do not call this
per chunk on large files.
Returns Promise<void>
Promise that resolves after two animation frames (or one timer tick).
Waits until after at least one paint (double rAF). Use sparingly — e.g. once before a long sync stretch so a loading overlay can appear. Do not call this per chunk on large files.