Move blink_perf.xml_http_request benchmark to tools/perf/contrib/ directory
* I verified that people still be able to run "./run_benchmark --browser=system blink_perf.xml_http_request" locally.
* Try bot run are in: https://build.chromium.org/p/tryserver.chromium.perf/builders/mac_10_12_perf_bisect/builds/149
Other effects of this:
_ People can run blink_perf.xml_http_request locally without needing to
pass "--also-run-disabled-benchmark"
_ The benchmarks' no-op run is no longer scheduled in perf waterfall,
hence the size reduction to the testing/buildbot/chrome.perf.* files
BUG=709063
Review-Url: https://codereview.chromium.org/2840213003
Cr-Commit-Position: refs/heads/master@{#467347}
12 files changed
