Resource Load Statistics: Don't create a WebResourceLoadStatisticsStore for ephemeral...

Resource Load Statistics: Don't create a WebResourceLoadStatisticsStore for ephemeral sessions
https://bugs.webkit.org/show_bug.cgi?id=187154
<rdar://problem/41487250>

Reviewed by Brent Fulgham and Chris Dumez.

Most of the changes in this patch remove the boolean parameter for tracking
ephemeral sessions and the IsReadOnly enum.

* UIProcess/API/Cocoa/WKWebsiteDataStore.mm:
(-[WKWebsiteDataStore _setResourceLoadStatisticsTestingCallback:]):
    Now returns early for ephemeral sessions.
* UIProcess/ResourceLoadStatisticsPersistentStorage.cpp:
(WebKit::ResourceLoadStatisticsPersistentStorage::ResourceLoadStatisticsPersistentStorage):
(WebKit::ResourceLoadStatisticsPersistentStorage::writeMemoryStoreToDisk):
(WebKit::ResourceLoadStatisticsPersistentStorage::scheduleOrWriteMemoryStore):
* UIProcess/ResourceLoadStatisticsPersistentStorage.h:
* UIProcess/WebResourceLoadStatisticsStore.cpp:
(WebKit::WebResourceLoadStatisticsStore::WebResourceLoadStatisticsStore):
* UIProcess/WebResourceLoadStatisticsStore.h:
* UIProcess/WebsiteData/WebsiteDataStore.cpp:
(WebKit::WebsiteDataStore::setResourceLoadStatisticsEnabled):
    Now returns early for ephemeral sessions.
(WebKit::WebsiteDataStore::enableResourceLoadStatisticsAndSetTestingCallback):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@233367 268f45cc-cd09-0410-ab3c-d52691b4dbfc