CodeHealth: Migrate `base::Value::FindKey()` to v2 API

Migrate `base::Value::FindKey()` to `base::Value::Dict::Find()` and
`base::Value::Dict::contains()` in -
/components/heap_profiling

This CL was uploaded by git cl split.

R=ssid@chromium.org

Bug: 1406815
Change-Id: Ic8a0ff9d2db57c75a974837be0d1758d25f78381
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4177091
Reviewed-by: Siddhartha S <ssid@chromium.org>
Auto-Submit: Kush Sinha <sinhak@chromium.org>
Commit-Queue: Kush Sinha <sinhak@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1095345}