Parameterized the type transformation warning messages and improved the check of the parameter count of the type transformation expressions
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=71616421
[NEW TYPE INFERENCE] Don't create unneeded NominalType instances for non-generic types.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=71616922
javascript/externs: add DOMImplementation#createHTMLDocument to externs
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=71630642
Fixed generator structure to close in on the spec (https://people.mozilla.org/~jorendorff/es6-draft.html#sec-generatorfunction-objects).

1. The @@iterator ($$iterator property until symbols are supported) property of a Generator returns the generator itself (so that a caller can call f().next() or f().$$iterator().next() and it will be exactly the same).
2. 'return x' in a generator function should yield {value: x, done: true} to the caller, unlike 'yield x' which yields {value: x, done: false} as we know that execution of the generator is completed after a return.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=71673322
Added support for parsing mapunion type transformation expressions with the form mapunion(Uniontype-Exp, (typevar) => TTL-Exp)
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=71675851