blobInfo.equals(BlobInfo.fromPb(blobInfo.toPb())) return false

While testing `StorageImpl` I noticed that:

``` java
BlobInfo blobInfo = BlobInfo.of("b", "n");
assertEquals(blobInfo, BlobInfo.fromPb(blobInfo.toPb()));
```

Was failing. 
Same problem also occurs with `BucketInfo`. 
In `BucketInfo` the `fromPb` method also throws NPE under some circumstances:

``` java
BucketInfo bucketInfo = BucketInfo.of("b");
BucketInfo.fromPb(bucketInfo.toPb());
```
