Disable deadline file in Android.

The deadline file is used to notify chrome the deadline string sent by
the server. This message allows chrome to take a different action based
on the urgency of the update. While we would like to provide a proper
API for this mechanism, it is rarely used in Chrome OS and doesn't work
on Android, so we disable it for now.

Bug: 24868621
Test: Unittest pass. No error message when tested on a dragonboard.

Change-Id: I77fc5b55e1c6ec79f12d88be40426058b8aa4d02
diff --git a/platform_constants_android.cc b/platform_constants_android.cc
index be0329b..b6ee29f 100644
--- a/platform_constants_android.cc
+++ b/platform_constants_android.cc
@@ -27,6 +27,8 @@
 const char kOmahaPlatformName[] = "Brillo";
 const char kUpdatePayloadPublicKeyPath[] =
     "/etc/update_engine/update-payload-key.pub.pem";
+// No deadline file API support on Android.
+const char kOmahaResponseDeadlineFile[] = "";
 
 }  // namespace constants
 }  // namespace chromeos_update_engine