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This replaces app state observing with tabbed activity observing. One
key difference is that tabbed activity does not include CCT. We only
want to preconnect DSE for non-CCT chrome foreground.

Bug: 1041118
Change-Id: I9e88e15c11cdfd7d13078a71c680be31c9b05932
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2006478
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Reviewed-by: Theresa  <twellington@chromium.org>
Reviewed-by: Robert Ogden <robertogden@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735128}