Launching tools/perf/run_benchmark fails with "ImportError: No module named psutil".

This is on my corp Mac desktop which I use for development.

Output:

tools/perf/run_benchmark try all-mac loading.desktop

Traceback (most recent call last):
  <module> at /Users/asvitkine/chromium/src/tools/perf/run_benchmark:9
    from core import trybot_command
  <module> at /Users/asvitkine/chromium/src/tools/perf/core/trybot_command.py:20
    from core import benchmark_finders
  <module> at /Users/asvitkine/chromium/src/tools/perf/core/benchmark_finders.py:10
    from core import perf_benchmark
  <module> at /Users/asvitkine/chromium/src/tools/perf/core/perf_benchmark.py:8
    from telemetry import benchmark
  <module> at /Users/asvitkine/chromium/src/third_party/catapult/telemetry/telemetry/benchmark.py:10
    from telemetry.internal import story_runner
  <module> at /Users/asvitkine/chromium/src/third_party/catapult/telemetry/telemetry/internal/story_runner.py:13
    from py_utils import memory_debug  # pylint: disable=import-error
  <module> at /Users/asvitkine/chromium/src/third_party/catapult/common/py_utils/py_utils/memory_debug.py:9
    import psutil
ImportError: No module named psutil

I worked around this issue by changing story_runner.py to comment out some lines:

#from py_utils import       #memory_debug.LogHostMemoryUsage()

  # pylint: disable=import-error