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onFailure is only invoked when the render frame has
been destroyed, but it is not really useful to
distinguish onComplete from onFailure in that case.
This also addresses the feedback that we received
from API Council.

This is a resubmit of CL 943633003

BUG=459539, 457184

Review URL: https://codereview.chromium.org/974483002

Cr-Commit-Position: refs/heads/master@{#319068}