This CL enables noImplicitReturns and noImplicitThis warnings in
TypeScript, another step on the road to stricter types.

Drive-by: Fix bug in search function.

Change-Id: Iafb528b5f0e7ccc8774bc218fd0dcdb206a0de31
Notry: true
Bug: v8:7327
Reviewed-on: https://chromium-review.googlesource.com/c/1396422
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58576}