print warning with line and column info

[baocang]

fixed https://github.com/Polymer/polymer-cli/issues/631

[rictic]

A bit of background first. Ideally we'd like to use the WarningPrinter from the analyzer, to get output like the linter gives, i.e.

          <link rel="import" href="./does-not-exist.html">
                                   ~~~~~~~~~~~~~~~~~~~~~

When we tried this last time though, we ran into trouble because we were analyzing some intermediate state, so the line numbers and column numbers didn't line up.

Getting better output here though would be a huge win, and I know @usergenic and @FredKSchott were making progress on that, so that we could use the WarningPrinter.

[rictic]

Have you tried this out in your build? Does this draw the squiggles in the right places?

[baocang]

@rictic I tried over our company project. and i also create a new project to test that. the squiggles in the right places but with more than one warning in single line, it draw the squiggles only the last one. I think this is not a big problem for use. Thanks for you did the WarningPrinter

is the line numbers and column numbers didn't line up has fixed?

[FredKSchott]

Now that analysis is happening before build, I think we actually are able to just use the analyzer's WarningPrinter

[rictic]

This looks good to me, please update the CHANGELOG. I'd recommend something like

 * Print build-time warnings and errors with full location information, and precise underlines of the place where the problem was identified.

[rictic]

Thanks for the PR!