Reimplement goog.collections.iterables.map() with ES6 for..of syntax.
Reimplement goog.collections.iterables.map() with ES6 for..of syntax.

Now that iterables.js is no longer ES5-only, the methods can be reimplemented
more simply with ES6 features.

RELNOTES: n/a

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=230554199

google/closure-library,google/closure-library,google/closure-library,google/closure-library,lucidsoftware/closure-library,lucidsoftware/closure-library,lucidsoftware/closure-library,google/closure-library,lucidsoftware/closure-library