Fix Print Preview failure state and add test

Prevent print preview error state from being unrecoverable by resetting
the state when the user selects a new printer. Add test to check that
the state resets and to check that the response to the INVALID_SETTINGS
event is correct.

BUG=708834
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2849733002
Cr-Commit-Position: refs/heads/master@{#468379}
2 files changed