chromeos: Roll system_api dep to 70e37fee.
chromeos: Roll system_api dep to 70e37fee.

This picks up new power manager constants for
screen-brightness-related method calls.

BUG=119743,chromium-os:26935
TEST=manual: it builds

Review URL: https://chromiumcodereview.appspot.com/9854007

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@128845 0039d316-1c4b-4281-b951-d872f2087c98

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