Replace MessageLoopProxy usage with ThreadTaskRunnerHandle in chrome/browser/password_manager module.

MessageLoopProxy is deprecated.
This basically does a search and replace:

MessageLoopProxy::current() -> ThreadTaskRunnerHandle::Get().

BUG=391045

Review URL: https://codereview.chromium.org/1125653002

Cr-Commit-Position: refs/heads/master@{#328281}
4 files changed