Document the 'int' return value of Resampler methods.
Document the 'int' return value of Resampler methods.

Remove an obsolete TODO comment.

R=andrew@webrtc.org
BUG=none

Review URL: https://webrtc-codereview.appspot.com/48589004

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#8814}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 4553941d32042326e79ae7483b6fab2908279869

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