[WV LES] Enable LES X-Client-Data for WV.

For Coronation project, it's important to understand the cross-talk
effects from experiments. We therefore need to enable LES for Rasta
Search experiments. This would allow WebView to use Rasta-HT-Colab for
apply HT corrections for Rasta metrics.

Bug: 263797385, 448562578
Change-Id: I555aa19a99f23808cafdaaea97943b49e92caed4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7028011
Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Rui Chen <chesterchen@google.com>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1537209}