Unresolved task detected: DependencyInfo "TODO(sdh): This would be better as a defender method once Java 8 is allowed (b/28382956)"

We found this task where the condition satisfied but action was not taken:

- src/com/google/javascript/jscomp/deps/DependencyInfo.java:186
```
// TODO(sdh): This would be better as a defender method once Java 8 is allowed (b/28382956):
// void DependencyInfo#writeAddDependency(Appendable);
```

- The trigger: "Java 8 is allowed" happened around commit <62ba0abf5ed74070a644284cb8e51d9e3d6dc9eb> (Oct 11 2017).

- But the action: "This would be better as a defender method" never happened since then.

- The new language features in Java 8 can be utilized, i.e. to add a default implementation for `writeAddDependency(Appendable)` in `interface DependencyInfo`.