Timing histogram for Read Aloud Tap to Seek

Adds a timing histogram to gauge how long Read Aloud Tap to Seek takes
from word selection to finding the substring match in the distilled
text.

Bug: 326113039
Change-Id: I351a055376b08a10e54d65029ad0dfb5fb9ff8ea
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5386248


Reviewed-by: Basia Zimirska <basiaz@google.com>
Commit-Queue: Andrea Gomez <andreaxg@google.com>
Cr-Commit-Position: refs/heads/main@{#1280276}