Fix analyzer's handling of import prefixes not followed by '.'.

Fix analyzer's handling of import prefixes not followed by '.'.

If 'p' is an import prefix, then 'p = ...' is treated as synonymous
with 'this.p = ...', and 'p()' is treated as synonymous with
'this.p()'.  In all other circumstances where 'p' is not followed by
'.', the spec calls for a compile time error.

Previous to this CL, 'p' not followed by '.' was being treated as
synonymous with 'this.p' under all circumstances.  This CL brings
analyzer in line with the spec, and updates the tests in
tests/language accordingly.

The VM and Dart2js currently fail to implement the compile-time error
properly.  See issues #23611 and #23612.

Fixes issue #23461.

R=scheglov@google.com

Committed: https://github.com/dart-lang/sdk/commit/fc83ce5ba97cf98fc628ab736c7cbf443ab0e93e

[Paul Berry, 2015-06-09 04:15:17]

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

[scheglov, 2015-06-09 05:54:09]

LGTM

[hausner, 2015-06-09 16:32:54]

hausner@google.com changed reviewers:
+ hausner@google.com

[hausner, 2015-06-09 16:32:55]

Thanks for filing the bug. I hope this is an oversight of the spec. Treating a
library prefix P differently on the right and left side of an assignment is
confusing. In other parts of the spec, P by itself is not a meaningful name.
E.g., P is not exported from a library even though it's declared in the library
scope.

[Paul Berry, 2015-06-09 20:38:58]

Committed patchset #1 (id:1) manually as
fc83ce5ba97cf98fc628ab736c7cbf443ab0e93e (presubmit successful).