update_engine: Report VPD write failure to UMA

Currently we see many first actives to come from non-FSI images. But we have not
been able to figure out why. This CL, reports a new error
kFirstActiveOmahaPingSentPersistenceError when writing the first active omaha
flag into VPD fails. This allows us to see if that is the actual cause of the
problem.

CL:1062659 adds the enum value on the Chrome side.

BUG=chromium:833980
TEST=unittests
TEST=precq

Change-Id: I65e233c5f895489ba905494fb20d7b00d0c4af10
Reviewed-on: https://chromium-review.googlesource.com/1062662
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
diff --git a/hardware_android.h b/hardware_android.h
index a6c9f6a..981f033 100644
--- a/hardware_android.h
+++ b/hardware_android.h
@@ -51,7 +51,7 @@
   bool GetNonVolatileDirectory(base::FilePath* path) const override;
   bool GetPowerwashSafeDirectory(base::FilePath* path) const override;
   bool GetFirstActiveOmahaPingSent() const override;
-  void SetFirstActiveOmahaPingSent() override;
+  bool SetFirstActiveOmahaPingSent() override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(HardwareAndroid);