History interface Go, Back, and Forward
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r? @asajeffrey
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implement go, forward, back
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Patches of File API
r? @Manishearth
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It's now set through the intermediate InterfaceConstructorBehavior structure,
which lets us improve the abstraction around NonCallbackInterfaceObjectClass
a bit better.
When the interface's constructor is supposed to always throw, the error for
calling `Foo()` without new is "Illegal constructor.". when the interface
actually defines an interface, the error is instead
"This constructor needs to be called with `new`.".
