Tweak iterations in HandleWatcherPerftest to reduce noise.
Tweak iterations in HandleWatcherPerftest to reduce noise.

The goal is to make tests take between 100ms and 1s to run.

Review URL: https://codereview.chromium.org/1452843004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#360162}

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