Check if dartdoc can run on the package.

[isoos]

First iteration for #269

[jakobr-google]

Doesn't this mean that we'll be generating the docs both in analyzer and dartdoc instances? If so, can we avoid doing the work twice? Maybe pull the dartdoc result in the analyzer client, and merge it into the analysis data?

[isoos]

Doesn't this mean that we'll be generating the docs both in analyzer and dartdoc instances? If so, can we avoid doing the work twice? Maybe pull the dartdoc result in the analyzer client, and merge it into the analysis data?

Yeah, this is likely the direction we are heading, although there are coordination issues, like: obsolete packages are not analyzed with pana, but are still running with dartdoc. Merging the two processing makes sense, but it requires more work on both pana (configurable/optional items in the analysis) and pub site (merging the two job processing).

For the immediate scope I think the ToolEnvironment parts should go in, and the actual running of dartdoc should be optional. I can split this PR or do a follow-up, whichever you prefer.

[jakobr-google]

sgtm, a follow-up PR is fine.

Code LGTM