Fix temporary directory path in Android.

We should use /data/misc/update_engine/tmp instead of /data/local/tmp.

Bug: 24478450
TEST=Delta update nolonger permission denied.

Change-Id: I9a8096e602320195d30147971def5145bd82d775
diff --git a/common/hardware_android.cc b/common/hardware_android.cc
index 4f06ff2..abfca44 100644
--- a/common/hardware_android.cc
+++ b/common/hardware_android.cc
@@ -21,16 +21,10 @@
 #include <cutils/properties.h>
 
 #include "update_engine/common/hardware.h"
+#include "update_engine/common/platform_constants.h"
 
 using std::string;
 
-namespace {
-
-// The stateful directory used by update_engine.
-const char kNonVolatileDirectory[] = "/data/misc/update_engine";
-
-}  // namespace
-
 namespace chromeos_update_engine {
 
 namespace hardware {
@@ -102,7 +96,7 @@
 }
 
 bool HardwareAndroid::GetNonVolatileDirectory(base::FilePath* path) const {
-  base::FilePath local_path(kNonVolatileDirectory);
+  base::FilePath local_path(constants::kNonVolatileDirectory);
   if (!base::PathExists(local_path)) {
     LOG(ERROR) << "Non-volatile directory not found: " << local_path.value();
     return false;