Clean up handling of declared/inferred types in ExecutableElementForLink

Clean up handling of declared/inferred types in ExecutableElementForLink

Reworked the `returnType` getter (which had complex logic that was
difficult to follow) in terms of two simpler getters:
`declaredReturnType` and `inferredReturnType`.  Also implemented logic
to ensure that inferred instance types are ignored when inferring
types of initializer expressions in the same library cycle (since the
linker is supposed to behave as if initializer expressions are
inferred first).

R=brianwilkerson@google.com, scheglov@google.com

Committed: https://github.com/dart-lang/sdk/commit/a771361120d98f94f417ee584d2d5afe80898184

[Paul Berry, 2016-04-19 16:33:27]

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

[scheglov, 2016-04-19 16:38:38]

LGTM

[Brian Wilkerson, 2016-04-19 16:40:29]

lgtm

[Paul Berry, 2016-04-19 16:47:49]

Description was changed from

==========
Clean up handling of declared/inferred types in ExecutableElementForLink

Reworked the `returnType` getter (which had complex logic that was
difficult to follow) in terms of two simpler getters:
`declaredReturnType` and `inferredReturnType`.  Also implemented logic
to ensure that inferred instance types are ignored when inferring
types of initializer expressions in the same library cycle (since the
linker is supposed to behave as if initializer expressions are
inferred first).
==========

to

==========
Clean up handling of declared/inferred types in ExecutableElementForLink

Reworked the `returnType` getter (which had complex logic that was
difficult to follow) in terms of two simpler getters:
`declaredReturnType` and `inferredReturnType`.  Also implemented logic
to ensure that inferred instance types are ignored when inferring
types of initializer expressions in the same library cycle (since the
linker is supposed to behave as if initializer expressions are
inferred first).

R=brianwilkerson@google.com, scheglov@google.com

Committed:
https://github.com/dart-lang/sdk/commit/a771361120d98f94f417ee584d2d5afe80898184
==========

[Paul Berry, 2016-04-19 16:47:50]

Committed patchset #1 (id:1) manually as
a771361120d98f94f417ee584d2d5afe80898184 (presubmit successful).