Add progress updates to FilesystemVerificationAction

An attempt to fix b/142525610. This CL adds progress reports to
FilesystemVerificationAction. So that clients(e.x. GMSCore) could
properly display a progress bar instead of hanging there for a
few minutes. GMSCore support is already done, see
https://critique-ng.corp.google.com/cl/317362455

Test: Did an OTA update and observed that verification progress
is ported from android OTA client
Bug: 142525610

Change-Id: I1cdb1970cb65fc767b49cd38650894eed4d90960
diff --git a/update_attempter_android.h b/update_attempter_android.h
index f8c78de..55003a0 100644
--- a/update_attempter_android.h
+++ b/update_attempter_android.h
@@ -37,6 +37,7 @@
 #include "update_engine/metrics_utils.h"
 #include "update_engine/network_selector_interface.h"
 #include "update_engine/payload_consumer/download_action.h"
+#include "update_engine/payload_consumer/filesystem_verifier_action.h"
 #include "update_engine/payload_consumer/postinstall_runner_action.h"
 #include "update_engine/service_delegate_android_interface.h"
 #include "update_engine/service_observer_interface.h"
@@ -47,6 +48,7 @@
     : public ServiceDelegateAndroidInterface,
       public ActionProcessorDelegate,
       public DownloadActionDelegate,
+      public FilesystemVerifyDelegate,
       public PostinstallRunnerAction::DelegateInterface,
       public CleanupPreviousUpdateActionDelegateInterface {
  public:
@@ -101,6 +103,9 @@
   bool ShouldCancel(ErrorCode* cancel_reason) override;
   void DownloadComplete() override;
 
+  // FilesystemVerifyDelegate overrides
+  void OnVerifyProgressUpdate(double progress) override;
+
   // PostinstallRunnerAction::DelegateInterface
   void ProgressUpdate(double progress) override;