Add flag to Dart VM --enable-checked-mode

[sethladd]

We talk about checked mode and production mode a lot, both in our documentation and in the spec. To keep things simple, I suggest adding an --enable-checked-mode flag to the VM, which turns on the behavior and semantics specified by what "checked mode" means.

I believe this is the same as --enable_type_checks and --enable_asserts

Ideally, this matches the same flags that can be given to Frog.

IN VM --enable_type_checks is the same flag as requested --enable_checked_mode: it turns on the type checks and enables asserts. We may want to rename --enable_type_checks to --enable_checked_mode to be consistent with naming in spec.

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Set owner to @crelier.

[crelier]

I'm afraid I do not like this proposed change. VM flags should have a more specific meaning than just "checked mode" and a finer granularity on what they control. Adding a new flag, rather than renaming an existing one is not much better, since it makes flags depending on each other. On the other hand, --enable_type_checks already turns on --enable_asserts, if I remember correctly.
   
Reassigning to Ivan for more opinion.

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Set owner to @iposva-google.

[sethladd]

Here's an example, from the spec, where "checked mode" means "turn on asserts":

"""
In checked mode, execution of an assert statement assert(e); proceeds as follows:
"""

[crelier]

After some discussion, it seems that keeping --enable_asserts and --enable_type_checks (but decoupling them), and adding a new --enable_checked_mode is the right solution.

Asserts would be evaluated if --enable_asserts or --enable_checked_mode.
Type checks would be performed if --enable_type_checks or --enable_checked_mode.

Let me know if this is acceptable.

[sethladd]

SGTM! Thanks for simplifying this. :)

[iposva-google]

Set owner to @crelier.
Added Accepted label.

[sethladd]

Frog just added --enable-checked-mode (notice dashes, not underscores)

[iposva-google]

Set owner to @iposva-google.

[iposva-google]

I did add support for --enable-checked-mode in the VM. That left me wondering whether we want to keep the name or whether we want to simplify to --checked-mode.

https://chromiumcodereview.appspot.com/9668034/

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Added Fixed label.