google / benchmark / 1651

92%

Pull #621

travis-ci

Add Iteration-related Counter::Flags. Fixes #618

Inspired by these [two](https://github.com/darktable-org/rawspeed/commit/a1ebe07be) [bugs](https://github.com/darktable-org/rawspeed/commit/0891555be) in my code due to the lack of those i have found fixed in my code:
* `kIsIterationInvariant` - `* state.iterations()`
  The value is constant for every iteration, and needs to be **multiplied** by the iteration count.
* `kAvgIterations` - `/ state.iterations()`
  The is global over all the iterations, and needs to be **divided** by the iteration count.

They play nice with `kIsRate`:
* `kIsIterationInvariantRate`
* `kAvgIterationsRate`.

I'm not sure how  meaningful they are when combined with `kAvgThreads`.
I guess the `kIsThreadInvariant` can be added, too, for symmetry with `kAvgThreads`.

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