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Previously, typing Ctrl-G would pop up the "find-text" box, appearing to be an alias for Ctrl-F.
Doing so will now highlight the page number in the viewer-page-selector, allowing for a quick and easy method to go to another page.
Changed viewer-page-selector to use a combination of paper-input-decorator and input instead of a sole paper-input. This affords us greater flexibility and should ease maintenance.

BUG=55920

Review URL: https://codereview.chromium.org/888343003

Cr-Commit-Position: refs/heads/master@{#314291}