Fix ill-formatted error messages in analyzer.

Fix ill-formatted error messages in analyzer.

Previously, two analyzer error messages (one recently introduced by
me, and one that has been around for a while) failed to provide enough
arguments to populate the error message template, resulting in
user-visible strings like "{0}" showing up in error messages.

This CL fixes the problem, and safeguards against it happening again
in the future by adding assertions to verify, at the time the error
message is formatted, that enough arguments were passed.

R=scheglov@google.com

Committed: https://code.google.com/p/dart/source/detail?r=44911

[Paul Berry, 2015-04-06 00:43:14]

paulberry@google.com changed reviewers:
+ scheglov@google.com

[scheglov, 2015-04-06 14:57:54]

LGTM

[Paul Berry, 2015-04-06 15:28:43]

Committed patchset #1 (id:1) manually as 44911 (presubmit successful).