Before the `ngDevMode` had to be set explicitly or it would throw
an exception at runtime. This changes it so that if `ngDevModu` is
`undefined` than we default to `ngDevMode = true`. In other words
unless the developer has explicitly asked to make a prodution build
by setting `ngDevMode = false` as compilation constant, the default
is `ngDevMode = true`.
This also fixes a minor bug where the setup code would read
`global['ngDevMode']` but all other code would read `global.ngDevMode`.
This would cause issues with closure compiler since the
reading of the `ngDevMode` must be consistent.
PR Close#25208
aafd502bcb