update_engine: Update libchrome APIS to r456626.

The new libchrome has been ported from Chromium and some APIs
have changed. Make necessary changes at call sites.

Change-Id: I8c3cea4510774c813a5d8fb10240918b5736884e
diff --git a/common/subprocess_unittest.cc b/common/subprocess_unittest.cc
index cbc9a85..10710e8 100644
--- a/common/subprocess_unittest.cc
+++ b/common/subprocess_unittest.cc
@@ -225,7 +225,7 @@
 TEST_F(SubprocessTest, CancelTest) {
   base::ScopedTempDir tempdir;
   ASSERT_TRUE(tempdir.CreateUniqueTempDir());
-  string fifo_path = tempdir.path().Append("fifo").value();
+  string fifo_path = tempdir.GetPath().Append("fifo").value();
   EXPECT_EQ(0, mkfifo(fifo_path.c_str(), 0666));
 
   // Start a process, make sure it is running and try to cancel it. We write