samples in doc should follow Dart code guidelines

[kwalrath]

A few things to check/change:

• use var, not type annotations, for local variables
• don't use double as a type
• use sentence case for comments (and punctuation)
• use lowercase_with_underscores for library and file names
• use => more often?

The rulez: http://www.dartlang.org/articles/style-guide/

[sethladd]

Added this to the M1 milestone.
Removed Type-Defect label.
Added Type-Enhancement label.

[kwalrath]

I've updated the language tour. More changes later...

[kwalrath]

I believe everything under my control has been updated to follow the guidelines. We can open more bugs later if we find pockets of noncompliant code.

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Added Fixed label.

[nicolasgarnier]

This issue has been moved to Github as part of a migration. Please use the Issue on Github going forward: https://github.com/dart-lang/dartlang.org/issues