Yapf could insert parentheses for better style

Sometimes, if we add parentheses to an expression, yapf gives a better reformatting. Here's an example.

Using this config:

```
[style]
dedent_closing_brackets = true
```

## Without surrounding parentheses

Input code:
```
if aaaaaaaaaaaaaaaaa(bbbbbbbbbbbbbbbbbb, ccccccccccccc) and dddddddddddddddd(eeeeeeeeeeeeeeeeee) == fffffffffffffffffffff:
pass
```

Reformatted by yapf:

```
if aaaaaaaaaaaaaaaaa(
bbbbbbbbbbbbbbbbbb, ccccccccccccc
) and dddddddddddddddd(eeeeeeeeeeeeeeeeee) == fffffffffffffffffffff:
pass
```

yapf reuses the parentheses of the aaa* function to keep the line continuation, which is clever, but it doesn't look as good as the next reformatting.

## With surrounding parentheses

I'm adding parentheses to the input code to "hint" yapf to reformat more:

```
if (aaaaaaaaaaaaaaaaa(bbbbbbbbbbbbbbbbbb, ccccccccccccc) and dddddddddddddddd(eeeeeeeeeeeeeeeeee) == fffffffffffffffffffff):
pass
```

yapf now gives the following output:

```
if (
aaaaaaaaaaaaaaaaa(bbbbbbbbbbbbbbbbbb, ccccccccccccc)
and dddddddddddddddd(eeeeeeeeeeeeeeeeee) == fffffffffffffffffffff
):
pass
```

which looks much better.

yapf should be able to add parentheses by itself.