Fix mime-handler-view crash upon creation:
We don't do create/attach steps through JavaScript API.

This broke after https://crrev.com/e7c9f7781cbc6db099dacbefdc19ac2fd9bfc19a
landed.

BUG=303491
Test=Open chrome with --out-of-process-pdf and --enable-mime-handler-view,
  Navigate to a PDF, renderer process shouldn't crash.

Review URL: https://codereview.chromium.org/638703004

Cr-Commit-Position: refs/heads/master@{#298572}
1 file changed