LegacyCurrentInstance (Common core for MPR versions 6.1.9 API)

```
public interface LegacyCurrentInstance
```
A facade type of interface to hide the differences of the v7 and v8 CurrentInstance implementation.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`clearAll()`	Clears all current instances.
`Map<Class<?>,com.vaadin.util.CurrentInstance>`	`getCurrentInstances()`	Get the all current instances.
`void`	`restoreInstances(Map<Class<?>,com.vaadin.util.CurrentInstance> previousInstances)`	Restores the given instances to the given values.

- Method Detail
  - getCurrentInstances
```
Map<Class<?>,com.vaadin.util.CurrentInstance> getCurrentInstances()
```
    Get the all current instances.
    This method is implemented in different ways for Vaadin 7 and Vaadin 8 to deal with API differences caused by dropping support for inheritable thread locals.
    
    Returns:
    
    a map from instance type to instance
  - clearAll
```
void clearAll()
```
    Clears all current instances.
  - restoreInstances
```
void restoreInstances(Map<Class<?>,com.vaadin.util.CurrentInstance> previousInstances)
```
    Restores the given instances to the given values. Note that this should only be used internally to restore Vaadin classes.
    
    Parameters:
    
    previousInstances - A Class-to-CurrentInstance map to set as current instances