Introduce classes for string and name indexes

Introduce classes for string and name indexes

In the VM's Kernel representation, introduce wrapper classes for
string and name indexes so it is obvious which one is which.  For
convenience there is an implicit conversion so that they can each be
used where an int is allowed.  However, there is no implicit
conversion _to_ either of these types.

BUG=
R=vegorov@google.com

Committed: https://github.com/dart-lang/sdk/commit/9935e86688a9624bbcb1e7b35c1e95af5c43c33e

[Kevin Millikin (Google), 2017-05-03 19:48:46]

kmillikin@google.com changed reviewers:
+ vegorov@google.com

[Vyacheslav Egorov (Google), 2017-05-03 19:54:10]

this is very nice! 

thanks for doing this.

lgtm

[Kevin Millikin (Google), 2017-05-03 22:43:26]

Description was changed from

==========
Introduce classes for string and name indexes

In the VM's Kernel representation, introduce wrapper classes for
string and name indexes so it is obvious which one is which.  For
convenience there is an implicit conversion so that they can each be
used where an int is allowed.  However, there is no implicit
conversion _to_ either of these types.

BUG=
==========

to

==========
Introduce classes for string and name indexes

In the VM's Kernel representation, introduce wrapper classes for
string and name indexes so it is obvious which one is which.  For
convenience there is an implicit conversion so that they can each be
used where an int is allowed.  However, there is no implicit
conversion _to_ either of these types.

BUG=
R=vegorov@google.com

Committed:
https://github.com/dart-lang/sdk/commit/9935e86688a9624bbcb1e7b35c1e95af5c43c33e
==========

[Kevin Millikin (Google), 2017-05-03 22:43:27]

Committed patchset #1 (id:1) manually as
9935e86688a9624bbcb1e7b35c1e95af5c43c33e (presubmit successful).