[omnibox chrome:omnibox] Export and Import JSON files

This CL adds a `Download as JSON` button to download the query inputs, display
inputs, and autocomplete responses to a .JSON file named
`omnibox_debug_export_<query>_<timestamp>.json`. This replaces the current
`Copy as JSON` button. The `Copy as Text` button, which only extracts the visual
output and not the entire responses or inputs, remains as is.

This CL also adds an `Import JSON` button to import previously exported JSON's.
Clicking the button will open a file selector; dragging the .JSON file or a
JSON string to the button also works. Selecting or dragging an invalid JSON file
or dragging an invalid JSON string results in a console.error message.

After successfully importing, a red 'Viewing imported data' warning will be
displayed under the import button to signify that the output may not reflect the
output the input would currently produce.

Bug: 891303
Change-Id: I1a17cda783fa9170baca8841bb80b19a3a67ab82
Reviewed-on: https://chromium-review.googlesource.com/c/1391917
Commit-Queue: manuk hovanesian <manukh@chromium.org>
Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620789}
5 files changed