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
#include "components/prefs/pref_service.h"
#include "content/common/devtools/devtools_network_conditions.h"
#include "content/common/devtools/devtools_network_controller.h"
#include "content/public/browser/browser_thread.h"
#include "content/public/browser/download_manager_delegate.h"
#include "content/public/browser/storage_partition.h"
#include "native_mate/dictionary.h"
#include "native_mate/object_template_builder.h"
#include "net/base/load_flags.h"
#include "net/disk_cache/disk_cache.h"
#include "net/dns/host_cache.h"
#include "net/http/http_auth_handler_factory.h"
#include "net/http/http_auth_preferences.h"
#include "net/proxy/proxy_config_service_fixed.h"
#include "net/proxy/proxy_service.h"
#include "net/url_request/static_http_user_agent_settings.h"
#include "net/url_request/url_request_context.h"
#include "net/url_request/url_request_context_getter.h"
#include "ui/base/l10n/l10n_util.h"
using atom::api::Cookies;
using content::BrowserThread;
using content::StoragePartition;
namespace {
struct ClearStorageDataOptions {
  GURL origin;
  uint32_t storage_types = StoragePartition::REMOVE_DATA_MASK_ALL;
  uint32_t quota_types = StoragePartition::QUOTA_MANAGED_STORAGE_MASK_ALL;
};
struct ClearAuthCacheOptions {
  std::string type;