Adds check/set for first_active_omaha_ping_sent (from vpd).

first_active_omaha_ping_sent is a boolean in RW_VPD that is checked to
decide whether to send the first active ping (a=-1) to omaha. update_engine
reads its value and sets it to "true" after first active ping is sent or
if the first ping has been sent already and it does not exits in the vpd
(to capture the same feature for older devices).

BUG=chromium:717788
TEST=cros_workon_make --test; Deployed on a device and made sure the
flag is read and writen properly.
CQ-DEPEND=CL:469126

Change-Id: I867d16de1d5d2da4d7a7e1f26aa8e951d90b68f2
Reviewed-on: https://chromium-review.googlesource.com/469107
Commit-Ready: Amin Hassani <ahassani@chromium.org>
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Andrew de los Reyes <adlr@chromium.org>
diff --git a/hardware_android.cc b/hardware_android.cc
index 91c3fbe..d4a6838 100644
--- a/hardware_android.cc
+++ b/hardware_android.cc
@@ -200,4 +200,14 @@
   return false;
 }
 
+bool HardwareAndroid::GetFirstActiveOmahaPingSent() const {
+  LOG(WARNING) << "STUB: Assuming first active omaha was never set.";
+  return false;
+}
+
+void HardwareChromeOS::SetFirstActiveOmahaPingSent() {
+  LOG(WARNING) << "STUB: Assuming first active omaha is never set.";
+  return;
+}
+
 }  // namespace chromeos_update_engine