Increase run count of paint benchmarks

The previous default run count was 5. It was small for frame time
measurement which may result in big variants. Increase the count
to 10 to reduce flakiness.

BTW rename dromaeoIterationCount to iterationCount, and provide
default value of warmUpCount for benchmarks measuring frame times.

Review-Url: https://codereview.chromium.org/2720663004
Cr-Commit-Position: refs/heads/master@{#453768}
16 files changed