arc: Abort booting ARC if the device is critically low on disk space.

chromeos/dbus/fake_cryptohome_client.cc

Index: chromeos/dbus/fake_cryptohome_client.cc
diff --git a/chromeos/dbus/fake_cryptohome_client.cc b/chromeos/dbus/fake_cryptohome_client.cc
index 1ec74fdbe3fafc50a73d9552e6ff2d17c978ea9f..f816dabd25f48e455c1215061982b3fb168cead7 100644
--- a/chromeos/dbus/fake_cryptohome_client.cc
+++ b/chromeos/dbus/fake_cryptohome_client.cc
@@ -116,6 +116,13 @@ void FakeCryptohomeClient::GetAccountDiskUsage(
   ReturnProtobufMethodCallback(reply, callback);
 }
 
+void FakeCryptohomeClient::GetFreeDiskSpace(
+    const GetFreeDiskSpaceCallback& callback) {
+  base::ThreadTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE,
+      base::Bind(callback, DBUS_METHOD_CALL_SUCCESS, 100 * 1024 * 1024));
+}
+
 void FakeCryptohomeClient::GetSystemSalt(
     const GetSystemSaltCallback& callback) {
   base::ThreadTaskRunnerHandle::Get()->PostTask(