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This was changed in the normal chromium print_preview_web_helper.cc in
02cfd5cc, but I missed the need to change it
in android's print_preview_web_helper.cc. This will allow isLoading() to live
solely on WebLocalFrame, as it doesn't make sense in a remote frame.

BUG=

Review URL: https://codereview.chromium.org/556923002

Cr-Commit-Position: refs/heads/master@{#294022}