Change name of 'signature' to ':signature' to not conflict with a DOM member.
Change name of 'signature' to ':signature' to not conflict with a DOM member.

Change-Id: Iff924ac9ef47abdb79d21a5eb9a9f69cf7135d28
Reviewed-on: https://dart-review.googlesource.com/45541
Reviewed-by: Sigmund Cherem <beaea8fd7d2a56555046ba4f362c8a93e3938576@google.com>

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