Add a GetCumulativeCPUUsage function to ProcessMetrics.

This also makes the GetPlatformIndependentCPUUsage function generic,
except for a couple of unsupported platforms that seem to retrieve
fractional CPU utilization directly from kernel.

Bug: 755840
Change-Id: I8254a1f1371d7d35d0eeec27f6f4efda03b0dbf9
Reviewed-on: https://chromium-review.googlesource.com/1058079
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Sigurður Ásgeirsson <siggi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#559110}

CrOS-Libchrome-Original-Commit: eb27eae7ba6d7ed839227d2f5912943a05a8b4fd
7 files changed
tree: 7925de8b796edb82eb9d88f797aa6fe034678f84
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/