[SurfacePolish] Updates search text in the fake search box on Start Surface during scrolling-up animation

This CL updates the size of the search box text to make it animate smoothly during the scrolling-up animation in Start Surface.

The summary of the change is shown in the following link:
https://drive.google.com/file/d/1c2O6pNS5IknWC5spyzRJrBxIcitD0-Cd/view?usp=sharing&resourcekey=0-4XWQTOizozpZc8_Hshfeug

Bug: 1492252
Change-Id: I0903ea5b4cc6e1e7681c4a7f924fb69d256d8fc0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4935339
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Commit-Queue: Xinyi Ji <xinyiji@chromium.org>
Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Reviewed-by: Xi Han <hanxi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1210476}