only wait for analysis if necessary when computing invocation suggestions

BUG=
R=scheglov@google.com

Review URL: https://codereview.chromium.org//728143002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41760 260f80e4-7a28-3924-810f-c04153c831b5
Use a better way to compute InterfaceTypes least upper bound.

R=brianwilkerson@google.com
BUG=

Review URL: https://codereview.chromium.org//730803003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41761 260f80e4-7a28-3924-810f-c04153c831b5