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.

BUG=chromium:724678
CQ-DEPEND=CL:480928
Test: Build.

Change-Id: I4dbaea4a2a19031375a8bf2415645a4f226dab57
diff --git a/hardware_chromeos_unittest.cc b/hardware_chromeos_unittest.cc
index a6bad54..162dec4 100644
--- a/hardware_chromeos_unittest.cc
+++ b/hardware_chromeos_unittest.cc
@@ -37,21 +37,22 @@
   void SetUp() override { ASSERT_TRUE(root_dir_.CreateUniqueTempDir()); }
 
   void WriteStatefulConfig(const string& config) {
-    base::FilePath kFile(root_dir_.path().value() + kStatefulPartition +
+    base::FilePath kFile(root_dir_.GetPath().value() + kStatefulPartition +
                          "/etc/update_manager.conf");
     ASSERT_TRUE(base::CreateDirectory(kFile.DirName()));
     ASSERT_TRUE(WriteFileString(kFile.value(), config));
   }
 
   void WriteRootfsConfig(const string& config) {
-    base::FilePath kFile(root_dir_.path().value() + "/etc/update_manager.conf");
+    base::FilePath kFile(root_dir_.GetPath().value() +
+                         "/etc/update_manager.conf");
     ASSERT_TRUE(base::CreateDirectory(kFile.DirName()));
     ASSERT_TRUE(WriteFileString(kFile.value(), config));
   }
 
   // Helper method to call HardwareChromeOS::LoadConfig with the test directory.
   void CallLoadConfig(bool normal_mode) {
-    hardware_.LoadConfig(root_dir_.path().value(), normal_mode);
+    hardware_.LoadConfig(root_dir_.GetPath().value(), normal_mode);
   }
 
   HardwareChromeOS hardware_;