compiler should be be independant of browser code

[DartBot]

This issue was originally filed by xdr...@gmail.com

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Request: Make the Dart->JS compiler as a seperate file from the browser checking code so that the project can be included in other projects such as Node.JS

[DartBot]

This comment was originally written by jat@google.com

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The compiler already is.

[DartBot]

This comment was originally written by drfibonacci@google.com

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Added Invalid label.