Roll src/third_party/cros_system_api/ 7d15090bd..57bbe676e (5 commits)

https://chromium.googlesource.com/chromiumos/platform/system_api.git/+log/7d15090bd036..57bbe676efe5

$ git log 7d15090bd..57bbe676e --date=short --no-merges --format='%ad %ae %s'
2018-02-12 derat system_api: Add powerd BacklightBrightnessChange protobuf.
2018-02-27 rjwright Make vm_concierge/service.proto optimize_for = LITE_RUNTIME
2018-02-23 dgreid vm_concierge: Add message to delete a vm disk
2018-01-02 benchan shill: add APN authentication property and value constants
2018-02-20 ejcaruso cryptohome: remove constant for CheckKey/AsyncCheckKey

Created with:
  roll-dep src/third_party/cros_system_api

Bug: 811138
Change-Id: Ie160210b32e587c6263a49b6f6db99eefae6926c
Reviewed-on: https://chromium-review.googlesource.com/951843Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Dan Erat <derat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541239}

DEPS

@@ -331,7 +331,7 @@ deps = {
 
   # For Linux and Chromium OS.
   'src/third_party/cros_system_api': {
-      'url': Var('chromium_git') + '/chromiumos/platform/system_api.git' + '@' + '7d15090bd03615b00e6ad070da5e85c0aa76aa13',
+      'url': Var('chromium_git') + '/chromiumos/platform/system_api.git' + '@' + '57bbe676efe5f394395c123d713968d104e878bf',
       'condition': 'checkout_linux',
   },