Update the postMessage function to match the Window.prototype.postMessage one.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=68220397
Added support for computed properties.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=68262232
Turn on typechecking for a transpilation test.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=68274906