Document strong mode

Document strong mode

See rendered markdown here:
 https://github.com/dart-lang/dev_compiler/blob/strong/STRONGMODE.md

Fixes #243

R=jmesserly@google.com, leafp@google.com

Committed: https://github.com/dart-lang/dev_compiler/commit/dbafa2e0a734d41cb664181c3927653285aec2be

[vsm, 2015-07-08 15:33:20]

vsm@google.com changed reviewers:
+ jmesserly@google.com, leafp@google.com

[Jennifer Messerly, 2015-07-08 15:44:02]

lgtm

https://codereview.chromium.org/1218993004/diff/1/STRONGMODE.md
File STRONGMODE.md (right):

https://codereview.chromium.org/1218993004/diff/1/STRONGMODE.md#newcode19
STRONGMODE.md:19: This document provides a high-level overview of strong mode. 
A corresponding formalism of strong mode can also be found
[here](http://www.google.com/url?q=http%3A%2F%2Fdart-lang.github.io%2Fdev_compiler%2Fstrong-dart.pdf&sa=D&sntz=1&usg=AFQjCNEHQ3EZiLkwUs1_ifoVu6R0HSrenw).
this link seems busted. Should be this?
https://dart-lang.github.io/dev_compiler/strong-dart.pdf

https://codereview.chromium.org/1218993004/diff/1/STRONGMODE.md#newcode53
STRONGMODE.md:53: ```javascript
fyi, I think "js" works too

https://codereview.chromium.org/1218993004/diff/1/STRONGMODE.md#newcode192
STRONGMODE.md:192: ```
```dart missing from this one? (it's there in others)

https://codereview.chromium.org/1218993004/diff/1/STRONGMODE.md#newcode466
STRONGMODE.md:466: - Disallow overriding fields: this results in complicated
generated code where a field definition in a subclass shadows the field
definition in a base class but both are generally required to be allocated. 
Users should prefer explicit getters and setters in such cases.  See:
https://github.com/dart-lang/dev_compiler/issues/52
I think "See issue #52" would auto link, because "#52" is magic :)

But if that does't work, maybe replace with a hyperlink?

[issue 52](https://github.com/dart-lang/dev_compiler/issues/52)

and below:

[issue 228](https://github.com/dart-lang/dev_compiler/issues/228)

[vsm, 2015-07-08 15:51:46]

https://codereview.chromium.org/1218993004/diff/1/STRONGMODE.md
File STRONGMODE.md (right):

https://codereview.chromium.org/1218993004/diff/1/STRONGMODE.md#newcode19
STRONGMODE.md:19: This document provides a high-level overview of strong mode. 
A corresponding formalism of strong mode can also be found
[here](http://www.google.com/url?q=http%3A%2F%2Fdart-lang.github.io%2Fdev_compiler%2Fstrong-dart.pdf&sa=D&sntz=1&usg=AFQjCNEHQ3EZiLkwUs1_ifoVu6R0HSrenw).
On 2015/07/08 15:44:02, John Messerly wrote:
> this link seems busted. Should be this?
> https://dart-lang.github.io/dev_compiler/strong-dart.pdf

Done.

https://codereview.chromium.org/1218993004/diff/1/STRONGMODE.md#newcode53
STRONGMODE.md:53: ```javascript
On 2015/07/08 15:44:02, John Messerly wrote:
> fyi, I think "js" works too

Acknowledged.

https://codereview.chromium.org/1218993004/diff/1/STRONGMODE.md#newcode192
STRONGMODE.md:192: ```
On 2015/07/08 15:44:02, John Messerly wrote:
> ```dart missing from this one? (it's there in others)

Done.

https://codereview.chromium.org/1218993004/diff/1/STRONGMODE.md#newcode466
STRONGMODE.md:466: - Disallow overriding fields: this results in complicated
generated code where a field definition in a subclass shadows the field
definition in a base class but both are generally required to be allocated. 
Users should prefer explicit getters and setters in such cases.  See:
https://github.com/dart-lang/dev_compiler/issues/52
On 2015/07/08 15:44:02, John Messerly wrote:
> I think "See issue #52" would auto link, because "#52" is magic :)
> 
> But if that does't work, maybe replace with a hyperlink?
> 
> [issue 52](https://github.com/dart-lang/dev_compiler/issues/52)
> 
> and below:
> 
> [issue 228](https://github.com/dart-lang/dev_compiler/issues/228)

Done - had to do the latter.

[Leaf, 2015-07-08 20:15:20]

lgtm.

https://codereview.chromium.org/1218993004/diff/20001/STRONGMODE.md
File STRONGMODE.md (right):

https://codereview.chromium.org/1218993004/diff/20001/STRONGMODE.md#newcode346
STRONGMODE.md:346: the runtime type is inferred as `List` in order to match the
context of the left hand side.  In other words, the code above executes as if it
was:
`List` should be `List<String>`?

[vsm, 2015-07-08 20:18:08]

https://codereview.chromium.org/1218993004/diff/20001/STRONGMODE.md
File STRONGMODE.md (right):

https://codereview.chromium.org/1218993004/diff/20001/STRONGMODE.md#newcode346
STRONGMODE.md:346: the runtime type is inferred as `List` in order to match the
context of the left hand side.  In other words, the code above executes as if it
was:
On 2015/07/08 20:15:20, Leaf wrote:
> `List` should be `List<String>`?

Done.

[vsm, 2015-07-08 20:18:27]

Committed patchset #3 (id:40001) manually as
dbafa2e0a734d41cb664181c3927653285aec2be (presubmit successful).