Roll src/third_party/cros_system_api/ 71adbf6a5..a71cda985 (4 commits)

https://chromium.googlesource.com/chromiumos/platform/system_api.git/+log/71adbf6a5686..a71cda985de2

$ git log 71adbf6a5..a71cda985 --date=short --no-merges --format='%ad %ae %s'
2018-08-22 semenzato system_api: dbus: add metrics_event protobuffer
2018-08-16 jkardatzke Add protobuf for mime type mappings in Crostini.
2018-08-22 chirantan seneschal: Update proto comments
2018-08-07 emaxx diagnostics: API for bootstrapping Mojo to browser

Created with:
  roll-dep src/third_party/cros_system_api

Bug: N/A
Change-Id: I7e5d49f74f31b8c959788cd3edd5a079f87ee315
Reviewed-on: https://chromium-review.googlesource.com/1197362Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Jeffrey Kardatzke <jkardatzke@google.com>
Cr-Commit-Position: refs/heads/master@{#587775}

DEPS

@@ -594,7 +594,7 @@ deps = {
 
   # For Linux and Chromium OS.
   'src/third_party/cros_system_api': {
-      'url': Var('chromium_git') + '/chromiumos/platform/system_api.git' + '@' + '71adbf6a56865ae5500686eaa221b0f988c3bada',
+      'url': Var('chromium_git') + '/chromiumos/platform/system_api.git' + '@' + 'a71cda985de20c747a6525de0fac2dc95766bd6d',
       'condition': 'checkout_linux',
   },