line breaking should be possible between alphanumeric and fullwidth opening punctuation

Test HTML+CSS at: http://jsbin.com/hobiko/edit?html,css,output
or:
```
<style>
p {
  width: 10em;
  background: yellow;
}
</style>
<p>あいうえおかきくけa「さしすせそ」</p>
<p>あいうえおかきくけ1「さしすせそ」</p>
```

What is the expected behavior?
Line breaking should occur as follows:

```
あいうえおかきくけa
「さしすせそ」

あいうえおかきくけ1
「さしすせそ」
```

What went wrong?
Line breaking occurs as follows:
```
あいうえおかきくけ
a「さしすせそ」

あいうえおかきくけ
1「さしすせそ」
```

It seems that line breaking is mistakenly prohibited between non-cjk letter or number and fullwidth opening punctuation such as "「".

[Radar WebKit Bug Importer]

<rdar://problem/39079754>