Fix a corner case of constant constructor dependency computation.

Fix a corner case of constant constructor dependency computation.

If a constant constructor does not contain an explicit call to
super(), and the base class lacks an explicit constructor, we need to
avoid marking the implicit base class constructor as a dependency,
since it is non-const.  (Note: this shouldn't occur very often in
real-world usage since is a compile-time error, but we still need to
be able to analyze it without throwing an exception).

Fixes the following test when the new task model is switched on:
co19/Language/07_Classes/6_Constructors/3_Constant_Constructors_A03_t02

R=brianwilkerson@google.com

Committed: https://github.com/dart-lang/sdk/commit/12696cafe9939cec03542b918bbc7019a9bff9a5

[Paul Berry, 2015-06-08 17:52:22]

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

[Brian Wilkerson, 2015-06-08 18:01:31]

LGTM

[Paul Berry, 2015-06-08 18:23:39]

Committed patchset #1 (id:1) manually as
12696cafe9939cec03542b918bbc7019a9bff9a5 (presubmit successful).