dart2js returns true for infinity is int

[DartBot]

This issue was originally filed by ngeoffray@google.com

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See test language/infinity_test.dart. dart2js uses Math.floor(x) == x for making an int check, and infinity returns true to that operation.

[kasperl]

Removed this from the Later milestone.

[kasperl]

Added this to the M2 milestone.

[karlklose]

This is also a problem for -0.0.

[peter-ahe-google]

Removed this from the M2 milestone.
Added this to the Later milestone.

[kasperl]

Added TriageForM5 label.

[kasperl]

Removed TriageForM5 label.

[kasperl]

Removed this from the Later milestone.
Added Oldschool-Milestone-Later label.

[kasperl]

Removed Oldschool-Milestone-Later label.