Avoid reading sourcemaps in js file if it is already in fileCoverage.inputSourceMap

[mttcr]

From #123
PR #87 allowed to use the inputSourceMap provided in fileCoverage. The problem is that we still parse the js file to override the sourcemap if there is one inlined. This PR skips the reading of the js file if we already have the sourcemap.

[dylans]

@MichaReiser any chance you have a moment to review/test this proposed follow-up to #87?

[dylans]

@mttcr note this is failing with our tests, see https://travis-ci.org/SitePen/remap-istanbul/builds/190977909

[MichaReiser]

Probably not to test, but I can review it. Let me know when the tests are fixed.

[mttcr]

I restored the codeIsArray logic and I provided a test that checks that the CoverageTransformer correctly uses the provided inputSourceMap and not the one inlined in the source. To check that, the inputSourceMap is a bit different from the inlined one: it has a custom sourceRoot. The test passes with my branch, and doesn't with yours.

@dylans @MichaReiser your tests are fixed and I also provided a new one to check the new functionality. Hope it's good for you!

[codecov-io]

Current coverage is 98.60% (diff: 100%)

Merging #125 into master will increase coverage by 0.17%

@@             master       #125   diff @@
==========================================
  Files            15         15          
  Lines           573        573          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits            564        565     +1   
+ Misses            9          8     -1   
  Partials          0          0          

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[MichaReiser]

Looks good from my side...

[dylans]

Thanks @mttcr and @MichaReiser . I'll let this sit for a few days in case anyone else has thoughts or feedback, and then land it.