In constant evaluation, consistently handle const depending on non-const.

In constant evaluation, consistently handle const depending on non-const.

It is a compile-time error for a constant value to depend on a
non-constant value (or a non-constant constructor), however the
analyzer still needs to be able to handle it.

This CL adjusts the ConstantEvaluationEngine so that it consistently
reports all the dependencies of a given constant (whether those
dependencies are constant are not), but which is tolerant of being
asked to compute a constant value of a non-constant.

Fixes test failures with the new task model enabled.  No behavioral
change with the new task model disabled.

R=brianwilkerson@google.com

Committed: https://github.com/dart-lang/sdk/commit/4e36247eeaec763406ca2b6a97986be47842b130

[Paul Berry, 2015-06-09 20:32:33]

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

[Paul Berry, 2015-06-09 20:32:34]

Brian--

This fixes the 4 errors in compile_time_error_code_test.dart with the new task
model turned on.  There are still many failures in that test, but I'm hoping
that many of the will be addressed by your changes which are blocked on this bug
fix.

[Brian Wilkerson, 2015-06-09 20:38:36]

LGTM

[Paul Berry, 2015-06-09 20:48:49]

Committed patchset #1 (id:1) manually as
4e36247eeaec763406ca2b6a97986be47842b130 (presubmit successful).