Steps:
1. Put some things in cache storage
2. Call `session.clearStorageData`

Expected:
Some way of clearing cache storage data

Actual:
No way of clearing cache storage data

This seems like it might just be missing an option, in `atom/browser/api/atom_api_session.cc#GetStorageMask` there are only options for some storages. What's missing is a way of setting any of these:
```
REMOVE_DATA_MASK_CACHE_STORAGE
REMOVE_DATA_MASK_PLUGIN_PRIVATE_DATA
```

* Electron version: 1.8.2
* Operating system: macos 10.13.3

Note: I didn't make a test app for this because it seems like the issue is obvious, let me know if you'd line one though.
atom/browser/api/atom_api_session.cc
base::Closure callback;
  args->GetNext(&callback);
  BrowserThread::PostTask(BrowserThread::IO, FROM_HERE,
      base::Bind(&ClearHostResolverCacheInIO,
                 WrapRefCounted(browser_context_->GetRequestContext()),
                 callback));
}
void Session::ClearAuthCache(mate::Arguments* args) {
  ClearAuthCacheOptions options;
  if (!args->GetNext(&options)) {
    args->ThrowError("Must specify options object");
    return;
  }
  base::Closure callback;
  args->GetNext(&callback);
  BrowserThread::PostTask(
      BrowserThread::IO, FROM_HERE,
      base::Bind(&ClearAuthCacheInIO,
                 WrapRefCounted(browser_context_->GetRequestContext()),
                 options, callback));
}
void Session::AllowNTLMCredentialsForDomains(const std::string& domains) {
  BrowserThread::PostTask(BrowserThread::IO, FROM_HERE,
      base::Bind(&AllowNTLMCredentialsForDomainsInIO,
                 WrapRefCounted(browser_context_->GetRequestContext()),
                 domains));
}
void Session::SetUserAgent(const std::string& user_agent,