Add disk cache options to Chrome
Add disk cache options to Chrome

Add `Chrome` options `disk_cache` and `disk_cache_size` which add chromium
options `--disk-cache-dir=<DIR>` and `--disk-cache-size=N` (bytes).
The default is to use `--disable-cache` (no disk caching).

There are two ways to use the new vars, if you just use
`Chrome(disk_cache=True)` the chromium cli option `--disable-cache` is
NOT used and chromium writes disk cache inside profile dir.

If you use `Chrome(disk_cache='/tmp/custom_dir', disk_cache_size=10000)`
chromium will use `--disk-cache-dir=/tmp/custom_dir
--disk-cache-size=10000`.

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