Support more checked mode compile time errors in analysis engine.

Support more checked mode compile time errors in analysis engine.

This changes the following errors to be checked mode compile time errors:

- LIST_ELEMENT_TYPE_NOT_ASSIGNABLE
- MAP_VALUE_TYPE_NOT_ASSIGNABLE
- MAP_KEY_TYPE_NOT_ASSIGNABLE

It also ensures that static warnings are always generated, so if the
analysis engine's client decides to disregard checked mode compile
time errors, the warnings won't be lost.

BUG=dartbug.com/16391
R=brianwilkerson@google.com, scheglov@google.com

Committed: https://code.google.com/p/dart/source/detail?r=40790

[Paul Berry, 2014-09-29 20:44:01]

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

[Brian Wilkerson, 2014-09-29 21:06:18]

LGTM

[scheglov, 2014-09-29 21:11:31]

LGTM

[Paul Berry, 2014-09-29 21:42:15]

Committed patchset #1 (id:1) manually as 40790 (presubmit successful).