[Sync] Add ClearServerData support to Sync Scheduler

sync/engine/sync_scheduler.h

Index: sync/engine/sync_scheduler.h
diff --git a/sync/engine/sync_scheduler.h b/sync/engine/sync_scheduler.h
index 37ca968c928341f46a96a7c43cca66ba48e253d3..4e5e694b94d1436ab003239b0a86c4a289575832 100644
--- a/sync/engine/sync_scheduler.h
+++ b/sync/engine/sync_scheduler.h
@@ -46,6 +46,14 @@ struct SYNC_EXPORT_PRIVATE ConfigurationParams {
   base::Closure retry_task;
 };
 
+struct SYNC_EXPORT_PRIVATE ClearParams {
+  ClearParams(const base::Closure& report_success_task);
+  ~ClearParams();
+
+  // Callback to invoke on successful completion.
+  base::Closure report_success_task;
+};
+
 class SYNC_EXPORT_PRIVATE SyncScheduler
     : public sessions::SyncSession::Delegate {
  public:
@@ -55,6 +63,10 @@ class SYNC_EXPORT_PRIVATE SyncScheduler
     // specific type only, and not continue syncing until we are moved into
     // normal mode.
     CONFIGURATION_MODE,
+    // This mode is used to issue a clear server data command.  The scheduler
+    // may only transition to this mode from the CONFIGURATION_MODE.  When in
+    // this mode, the only schedulable operation is |SchedulerClearServerData|.
+    CLEAR_SERVER_DATA_MODE,
     // Resumes polling and allows nudges, drops configuration tasks.  Runs
     // through entire sync cycle.
     NORMAL_MODE,
@@ -81,6 +93,11 @@ class SYNC_EXPORT_PRIVATE SyncScheduler
   // Note: must already be in CONFIGURATION mode.
   virtual void ScheduleConfiguration(const ConfigurationParams& params) = 0;
 
+  // Schedules clear of server data in preparation for transitioning to
+  // passphrase encryption. The scheduler must be in CLEAR_SERVER_DATA_MODE
+  // before calling this method.
+  virtual void ScheduleClearServerData(const ClearParams& params) = 0;
+
   // Request that the syncer avoid starting any new tasks and prepare for
   // shutdown.
   virtual void Stop() = 0;