support --disk-cache-size flag

[cjld]

I find out that the implementation of CreateHttpCacheBackendFactory, does not use the switch (--disk-cache-size=...), it set the cache size to zero, cause the cache size caculate by net::HttpCache::DefaultBackend and ignore the switch.

[deepak1556]

--disk-cache-size is a chrome specific flag and hence wasn't implemented by default. There was already request in Electron for this flag electron/electron#7713 . If you are interested to implement it, feel free to send a PR. Thanks!

[cjld]

It is worked for me.
hope this PR could help!