llvm-cov show HTML: Inconsistent results between per-file indices and each source file view

[chapuni]

Apparently, line counts differ with expansions. The index doesn't look up header files that don't include functions but macros.

I guess actually the difference would come from the behavior difference between getCoverageForFile (source view) and getCoverageForFunction (reports and indices).

I think the index should use getCoverageForFile.