Migrate WaitableEvent to enum-based constructor in tools/

Change automated with clang-tidy (details @ https://crbug.com/612843#c13)

BUG=612843

Review-Url: https://codereview.chromium.org/2023003005
Cr-Original-Commit-Position: refs/heads/master@{#397225}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 3dbb1f62a6fbc115a027294b982db68d3d21012f