GitLab

- NSObject's NS_DESIGNATED_INITIALIZER -init method requires
   an -init NS_UNAVAILABLE implementation.
- Correct nonnull API usage.
- Cast to NSInteger for comparisons with NSNotFound.
- Account for dylib -> tbd change in latest Xcode.

BUG=498581, 498825, 498841

Review URL: https://codereview.chromium.org/1171203004

Cr-Commit-Position: refs/heads/master@{#333756}