Add check for backup in cloud.

Signal/src/util/OWSBackup.h

@@ -6,6 +6,9 @@ NS_ASSUME_NONNULL_BEGIN
 
 extern NSString *const NSNotificationNameBackupStateDidChange;
 
+typedef void (^OWSBackupBoolBlock)(BOOL success);
+typedef void (^OWSBackupErrorBlock)(NSError *error);
+
 typedef NS_ENUM(NSUInteger, OWSBackupState) {
     // Has never backed up, not trying to backup yet.
     OWSBackupState_Idle = 0,

Signal/src/util/OWSBackup.m

@@ -5,6 +5,7 @@
 #import "OWSBackup.h"
 #import "NSNotificationCenter+OWS.h"
 #import "OWSBackupExport.h"
+#import "Signal-Swift.h"
 #import <Curve25519Kit/Randomness.h>
 #import <SignalServiceKit/AppContext.h>
 #import <SignalServiceKit/NSDate+OWS.h>
@@ -129,6 +130,8 @@ NS_ASSUME_NONNULL_BEGIN
     return result;
 }
 
+#pragma mark - Backup Export
+
 - (void)setLastExportSuccessDate:(NSDate *)value
 {
     OWSAssert(value);
@@ -267,6 +270,26 @@ NS_ASSUME_NONNULL_BEGIN
     }
 }
 
+#pragma mark - Backup Import
+
+- (void)checkCanImportBackup:(OWSBackupBoolBlock)success failure:(OWSBackupErrorBlock)failure
+{
+    OWSAssertIsOnMainThread();
+
+    DDLogInfo(@"%@ %s", self.logTag, __PRETTY_FUNCTION__);
+
+    [OWSBackupAPI checkForManifestInCloudWithSuccess:^(BOOL value) {
+        dispatch_async(dispatch_get_main_queue(), ^{
+            success(value);
+        });
+    }
+        failure:^(NSError *error) {
+            dispatch_async(dispatch_get_main_queue(), ^{
+                failure(error);
+            });
+        }];
+}
+
 #pragma mark -
 
 - (void)applicationDidBecomeActive:(NSNotification *)notification