FIRTransactionResult
@interface FIRTransactionResult : NSObjectUsed for runTransactionBlock(_:). A TransactionResult instance is a
container for the results of the transaction.
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                  Used for runTransactionBlock(_:). Indicates that the new value should be saved at this location.DeclarationObjective-C + (nonnull FIRTransactionResult *)successWithValue: (nonnull FIRMutableData *)value;ParametersvalueA MutableDatainstance containing the new value to be setReturn ValueA TransactionResultinstance that can be used as a return value from the block given torunTransactionBlock(_:).
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                  Used for runTransactionBlock(_:). Indicates that the current transaction should no longer proceed.DeclarationObjective-C + (nonnull FIRTransactionResult *)abort;Return ValueA TransactionResultinstance that can be used as a return value from the block given torunTransactionBlock(_:)