Relax assertion on setNativeName.

BUG=
R=herhut@google.com

Review URL: https://codereview.chromium.org//508053003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@39723 260f80e4-7a28-3924-810f-c04153c831b5
Fix refactoring of canHit.

BUG=
R=herhut@google.com

Review URL: https://codereview.chromium.org//512803002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@39724 260f80e4-7a28-3924-810f-c04153c831b5
Introduce PlaceholderTypeInformation to properly model placeholders during type graph construction.

BUG=
R=johnniwinther@google.com

Review URL: https://codereview.chromium.org//510723002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@39725 260f80e4-7a28-3924-810f-c04153c831b5