Support using an externally manage list of images in UrlDataManager for wasm debugger.

Bug: skia:9746
Change-Id: I07b5fe1f8f4250e29153b71ce2be106461f09928
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/261998
Commit-Queue: Nathaniel Nifong <nifong@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
4 files changed