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Follow-on to crrev.com/c/1823801.

From crbug.com/1000936, failures in doing conversion of PDF for Nup
caused the Print Preview UI to endlessly spin in the
"Loading preview ..." state without ever showing that it had failed.

Similar behavior can be replicated during development by inducing
crashes in PDF composition calls inside PdfCompositorImpl.

Wrap the PDF page composition calls' callbacks with
mojo::WrapCallbackWithDefaultInvokeIfNotRun() so that a status is
provided even if the utility process disappears before completing.

Update the On<composite-something>Done() callbacks to include a
notification call to the Print Preview UI to report errors.

Bug: 1003171
Change-Id: Id351cefd5d91b322a915fa635865969e1cbb1142
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1825661Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Alan Screen <awscreen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700021}