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- Hide and disable the sidenav in annotation mode.
- Fix a timing issue, where the annotations bar would briefly appear
  when the annotation mode was toggled before disappearing and then
  re-appearing when the ink controller finished loading.
- Fix a positioning issue in which the document scrolled slightly when
  changing between annotation mode and the plugin.
- With the third fix above, positioning is much closer to expectations
  in the annotations feature enabled test. Verified that scrolling/zoom
  seems correct now, and updated the mismatched expectation for the
  case of the update being enabled as recommended by the test's original
  author.

Bug: 1124183
Change-Id: I8f9357d883088e31fc8882f3359e662685978de0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2405539
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806882}