Restore kPausePostRequest event handling
Restore kPausePostRequest event handling

Fixes https://github.com/flutter/flutter/issues/10934#issuecomment-312134244

Related https://github.com/dart-lang/sdk/commit/94a9061925ed222cf3f954aabc3dd90f9e9f4ca0

BUG=
R=asiva@google.com

Review-Url: https://codereview.chromium.org/2979193002 .

dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk