Incorrect frog type warning

[dgrove]

with bleeding_edge r1660, this code yields a warning:

import("dart:html");

main() {
 ImageElement e = new Element.tag("img");
}

./frogsh --compile-only i.dart
i.dart:4:19: warning: type "ElementWrappingImplementation" is not assignable to "ImageElement"
 ImageElement e = new Element.tag("img");
                  ^^^^^^^^^^^^^^^^^^^^^^

The warning is incorrect.

[DartBot]

This comment was originally written by [email protected]

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Added Triaged label.

[jmesserly]

Added Fixed label.