Add per-target zinc compile stats

[stuhood]

Problem

Visibility into the size and compile time of individual JVM targets is currently not great. While log parsing is possible, it's not scalable for this usecase.

Solution

Now that we have an API for recording target information, begin recording zinc compilation info.

Result

The target_data entry in the posted JSON stats contains information like the following:

 'src/scala/org/pantsbuild/zinc/analysis:analysis': {
    u'compile.zinc': {
        u'compile': {
            u'classpath_len': 54,
             'sources_len': 3,
             'incremental': False,
             'time': 6.252178907394409
        }
    }
},
 'src/scala/org/pantsbuild/zinc/extractor:extractor': {
    u'compile.zinc': {
        u'compile': {
            u'classpath_len': 61,
             'sources_len': 3,
             'incremental': False,
             'time': 6.599011182785034
        }
    }
},

... in addition to any data recorded by junit.

[kwlzn]

lgtm!

[benjyw]

Maybe use the Timer class from pants.util.contextutil?

[benjyw]

Maybe use the Timer class from pants.util.contextutil?

[baroquebobcat]

Looks pretty good!
Just a couple comments, but I don't consider them blocking.

• Could you note specifically what info you are adding to the reporting in the summary?
• Also, I'd like to see tests for this if possible.

[mateor]

I cannot wait to use this. Thanks stu!