id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
685825824,MDU6SXNzdWU2ODU4MjU4MjQ=,4376,wrong chunk sizes in html repr with nonuniform chunks,2448579,open,0,,,3,2020-08-25T21:23:11Z,2020-10-07T11:11:23Z,,MEMBER,,,,"<!-- Please include a self-contained copy-pastable example that generates the issue if possible.

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Bug reports that follow these guidelines are easier to diagnose, and so are often handled much more quickly.
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**What happened**:

The HTML repr is using the first element in a chunks tuple;

**What you expected to happen**:

 it should be using whatever dask does in this case

**Minimal Complete Verifiable Example**:

```python

import xarray as xr
import dask


test = xr.DataArray(
    dask.array.zeros(
        (12, 901, 1001),
        chunks=(
            (1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1),
            (1, 899, 1),
            (1, 199, 1, 199, 1, 199, 1, 199, 1, 199, 1),
        ),
    )
)
test.to_dataset(name=""a"")
```

![image](https://user-images.githubusercontent.com/2448579/91229202-fbebfe00-e718-11ea-9127-8b7364976762.png)

EDIT: The text repr has the same issue
```
<xarray.Dataset>
Dimensions:  (dim_0: 12, dim_1: 901, dim_2: 1001)
Dimensions without coordinates: dim_0, dim_1, dim_2
Data variables:
    a        (dim_0, dim_1, dim_2) float64 dask.array<chunksize=(1, 1, 1), meta=np.ndarray>
```","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/4376/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,issue