[Sync] Initial support for encrypting any datatype (no UI hookup yet).

chrome/browser/sync/glue/sync_backend_host.h

Index: chrome/browser/sync/glue/sync_backend_host.h
diff --git a/chrome/browser/sync/glue/sync_backend_host.h b/chrome/browser/sync/glue/sync_backend_host.h
index 01954a570cd1786f9dd7ce8c4e933491c6e7cfc2..3825f87b33df676bb949b0400ee32fb5b94a766d 100644
--- a/chrome/browser/sync/glue/sync_backend_host.h
+++ b/chrome/browser/sync/glue/sync_backend_host.h
@@ -84,6 +84,9 @@ class SyncFrontend {
   // encrypted using the accepted passphrase.
   virtual void OnPassphraseAccepted() = 0;
 
+  virtual void OnEncryptionComplete(
+      const syncable::ModelTypeSet& encrypted_types) = 0;
+
  protected:
   // Don't delete through SyncFrontend interface.
   virtual ~SyncFrontend() {
@@ -154,6 +157,14 @@ class SyncBackendHost : public browser_sync::ModelSafeWorkerRegistrar {
       const syncable::ModelTypeSet& types,
       CancelableTask* ready_task);
 
+  // Encrypts the specified datatypes and marks them as needing encryption on
+  // other machines. This affects all machines synced to this account and all
+  // data belonging to the specified types. |encrypted_types| must be a subset
+  // of the enabled datatypes.
+  // Note: actual work is done on core_thread_'s message loop.
+  virtual void EncryptDataTypes(
+      const syncable::ModelTypeSet& encrypted_types);
+
   syncable::AutofillMigrationState
       GetAutofillMigrationState();
 
@@ -259,6 +270,8 @@ class SyncBackendHost : public browser_sync::ModelSafeWorkerRegistrar {
     virtual void OnUpdatedToken(const std::string& token);
     virtual void OnClearServerDataFailed();
     virtual void OnClearServerDataSucceeded();
+    virtual void OnEncryptionComplete(
+        const syncable::ModelTypeSet& encrypted_types);
 
     struct DoInitializeOptions {
       DoInitializeOptions(
@@ -310,6 +323,10 @@ class SyncBackendHost : public browser_sync::ModelSafeWorkerRegistrar {
     // on behalf of SyncBackendHost::SupplyPassphrase.
     void DoSetPassphrase(const std::string& passphrase, bool is_explicit);
 
+    // Called on SyncBackendHost's |core_thread_| to set the datatypes we need
+    // to encrypt as well as encrypt all local data of that type.
+    void DoEncryptDataTypes(const syncable::ModelTypeSet& encrypted_types);
+
     // The shutdown order is a bit complicated:
     // 1) From |core_thread_|, invoke the syncapi Shutdown call to do a final
     //    SaveChanges, close sqlite handles, and halt the syncer thread (which
@@ -398,6 +415,11 @@ class SyncBackendHost : public browser_sync::ModelSafeWorkerRegistrar {
     // Invoked when an updated token is available from the sync server.
     void NotifyUpdatedToken(const std::string& token);
 
+    // Invoked when sync finishes encrypting new datatypes or has become aware
+    // of new datatypes requiring encryption.
+    void NotifyEncryptionComplete(const syncable::ModelTypeSet&
+                                      encrypted_types);
+
     // Called from Core::OnSyncCycleCompleted to handle updating frontend
     // thread components.
     void HandleSyncCycleCompletedOnFrontendLoop(
@@ -461,7 +483,6 @@ class SyncBackendHost : public browser_sync::ModelSafeWorkerRegistrar {
   scoped_refptr<Core> core_;
 
  private:
-
   UIModelWorker* ui_worker();
 
   void ConfigureAutofillMigration();