Add flag guarded strings updates for high efficiency dialog

We are going to display updated strings when we launch the new version
of the dialog. This change adds placeholders for the title/body text
as well as the label below the gauge chart.

Bug: 1424230
Change-Id: Ifc477a021b1195764958a59b00d887b33d44a3eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4555986


Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Eshwar Stalin <estalin@chromium.org>
Commit-Queue: Alison Gale <agale@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1148540}