Roll src/third_party/cros_system_api/ 53717bc2d..47afcabaf (3 commits)

https://chromium.googlesource.com/chromiumos/platform/system_api.git/+log/53717bc2de48..47afcabaf957

$ git log 53717bc2d..47afcabaf --date=short --no-merges --format='%ad %ae %s'
2017-10-25 derat system_api: Add powerd ScreenIdleState proto.
2017-10-25 ejcaruso shill: make property identifier for Cellular.ModelID consistent
2017-10-02 ejcaruso switches: add modemfwd_switches.h

Created with:
  roll-dep src/third_party/cros_system_api

Bug: 778449
Change-Id: Ifaefefa117c08d824e1bf1125037f6e6fad1105b
Reviewed-on: https://chromium-review.googlesource.com/742231Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Dan Erat <derat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512598}

DEPS

@@ -274,7 +274,7 @@ deps = {
 
   # For Linux and Chromium OS.
   'src/third_party/cros_system_api': {
-      'url': Var('chromium_git') + '/chromiumos/platform/system_api.git' + '@' + '53717bc2de485531ef39c439edaf35a264cb2fb7',
+      'url': Var('chromium_git') + '/chromiumos/platform/system_api.git' + '@' + '47afcabaf957c013418ef2a33481ec1fe764dc94',
       'condition': 'checkout_linux',
   },