Previously I added parens everywhere to make this @proxy() because our typing indicated
it was a function that returned a decorator, but this breaks dart. Instead, the typing needs
to be changed.
Fixes#3494
This change also makes us compliant with 1.6.0-dev compiler,
so we can do some experiments with apps that use 1.6 features
and compile against Angular.
We should probably add a travis build for 1.6 so we stay compatible
with both versions.