Verity writes propogate progress report

Test: tested on cuttlefish device with inc_ota from build 9263663 9419942. Ensured progress grows linearly from 0 - 0.6. Half time spent in read step, half in Verity Writes.
Change-Id: Iffa16571e828909cd6ac58f262736c0b6ca7b066
diff --git a/payload_consumer/verity_writer_android.h b/payload_consumer/verity_writer_android.h
index 0d48803..1aaafd5 100644
--- a/payload_consumer/verity_writer_android.h
+++ b/payload_consumer/verity_writer_android.h
@@ -55,6 +55,7 @@
   void UpdateState();
   bool Finished() const;
   void Reset();
+  double ReportProgress() const;
 
  private:
   brillo::Blob rs_blocks_;
@@ -88,7 +89,7 @@
   bool Finalize(FileDescriptor* read_fd, FileDescriptor* write_fd) override;
   bool IncrementalFinalize(FileDescriptor* read_fd,
                            FileDescriptor* write_fd) override;
-
+  double GetProgress() override;
   bool FECFinished() const override;
   // Read [data_offset : data_offset + data_size) from |path| and encode FEC
   // data, if |verify_mode|, then compare the encoded FEC with the one in