Issue 2373. 'v is Unknown' is compile-time warning, not error

Issue 2373. 'v is Unknown' is compile-time warning, not error
http://code.google.com/p/dart/issues/detail?id=2373

...but 'v is Known<No, Paramaters>' is error.
Illogical, but so says the Spec.


R=brianwilkerson@google.com
BUG=
TEST=

Committed: https://code.google.com/p/dart/source/detail?r=8872

[Brian Wilkerson, 2012-06-19 16:16:51]

LGTM, though you might want to hold off a little before committing to see
whether you get a response to your e-mail (in case the spec is wrong here).

https://chromiumcodereview.appspot.com/10536203/diff/1/compiler/javatests/com...
File
compiler/javatests/com/google/dart/compiler/type/TypeAnalyzerCompilerTest.java
(right):

https://chromiumcodereview.appspot.com/10536203/diff/1/compiler/javatests/com...
compiler/javatests/com/google/dart/compiler/type/TypeAnalyzerCompilerTest.java:2687:
public void test_unknownIsType() throws Exception {
nit: I would prefer to see this named "test_isType_unknown" for consistency.

[scheglov, 2012-06-19 21:17:32]

> LGTM, though you might want to hold off a little before committing to see
> whether you get a response to your e-mail (in case the spec is wrong here).

I've got confirmation from Gilad that spec is correct.

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  So, using not existing type for check is OK (warning), but using existing type
incorrectly is error?

Yes.   I've explained why this is the case. 
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