Calling an undefined constructor via new is a warning, not an error

[gbracha]

See issue #1031.

Latest version of spec, section 10.10.1 replaces errors with warnings in cases where the class or the constructor is undeclared. Motivation is similar to other cases: do not impose workflow - just warn and make it a dynamic error.

"Let e be a new expression of the form new T.id(a1, .., an, xn+1: an+1, …, xn+k: an+k) or the form new T(a1, .., an, xn+1: an+1, …, xn+k: an+k). It is a static warning if T is not a class or interface accessible in the current scope, optionally followed by type arguments.

If e is of the form new T.id(a1, .., an, xn+1: an+1, …, xn+k: an+k) it is a static warning if T.id is not the name of a constructor declared by the type T. If e of the form new T(a1, .., an, xn+1: an+1, …, xn+k: an+k) it is a static warning if the type T does not declare a constructor with the same name as the declaration of T.
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[scheglov]

Added Waiting label.

[bwilkerson]

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[scheglov]

Set owner to @scheglov.
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[scheglov]

https://chromiumcodereview.appspot.com/10829288

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[scheglov]

https://code.google.com/p/dart/source/detail?r=10531

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