Introduce the Error object class in the vm. It represents all of the

Introduce the Error object class in the vm. It represents all of the
things that may go wrong while invoking the dart api.

Here are the four types of error:

- ApiError = the user misused one of the dart apis
- LanguageError = a language-level problem, e.g. compiler error
- UnhandledException = an uncaught exception made its way to the embedder
- UnwindError = a forced isolate interrupt

This cl is the first of a series. I plan to move the point of
creation for LanguageErrors into the Parser, etc. I also plan to move
the longjmp's out of dart_api_impl.cc. I also also plan to implement
UnwindErrors later.

(Copied from Issue 9085031 due to subversion problems)
Committed: https://code.google.com/p/dart/source/detail?r=3168

[turnidge, 2012-01-10 21:35:22]

TBR -iposva

This is the same cl that you have already reviewed but patched into a new
client.

Todd