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These features (tab switch suggestions, new answer layout and rich
entities) all work without the MD Refresh UI, but the layout looks
weird. It's not something we'd want to launch. So this change disables
them if the MD Refresh UI is not also enabled.

The intent in taking this approach (vs. just enabling the correct
combination of flags manually or via experiment config) is two-fold:
1. Ensure that when we start experiments on these, if the MD Refresh UI
   is turned off, these features will automatically be turned off as
   well for users in the experimental group.
2. Prevent people from enabling the new features without MD Refresh and
   then filing bugs for a configuration that we don't intend to support.

Change-Id: Ie29ba598ae04a4d5e14437d0dd8d5e189815ef40
Reviewed-on: https://chromium-review.googlesource.com/1103152Reviewed-by: Tommy Li <tommycli@chromium.org>
Commit-Queue: Justin Donnelly <jdonnelly@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568005}