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Modifies the HatsDialog to use trigger ID instead of site ID to load the
surveys. It also modifies loading the survey as a dialog instead of a
window with frame buttons, since the HTML survey already includes a
close button.

NOTE: This is a reupload of a previously abandoned CL. This approach may
have possible points of failure:
  - Survey may not load, leaving user with a blank window.
  - Allowed survey localizations may not match the device locale.
  - HaTS backend may choose to not load the survey.
Subsequent work will fix this issues. See go/cros-hats-next follow-up
work section.

Bug: 1087034
Test: Tested manually on linux chrome and atlas
Change-Id: I1453617284fcf1e30c8107643a763b7880fa3c73
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2386418
Commit-Queue: Malay Keshav <malaykeshav@chromium.org>
Reviewed-by: Xiyuan Slow <xiyuan@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803749}