appcache: delete appcache directory from profile when disabled

Once AppCache has been removed from Chrome, sites will have no way of
cleaning up user data in local profiles.  To fix this, when a storage
partition is accessed when AppCache has been disabled, we will delete
the AppCache directory from that profile directory.

Bug: 1081897
Change-Id: Iea404f7c83595ba1397fab4a5d3f97d1e3280916
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2343588
Commit-Queue: enne <enne@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#796938}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: bd17f198378256de880e54544a6076de1215b854

blink/common/features.cc

@@ -581,7 +581,8 @@ const base::FeatureParam<DelayAsyncScriptDelayType>
 
 // The AppCache feature is a kill-switch for the entire AppCache feature,
 // both backend and API.  If disabled, then it will turn off the backend and
-// api, regardless of the presence of valid origin trial tokens.
+// api, regardless of the presence of valid origin trial tokens.  Disabling
+// AppCache will also delete any AppCache data from the profile directory.
 const base::Feature kAppCache{"AppCache", base::FEATURE_ENABLED_BY_DEFAULT};
 // If AppCacheRequireOriginTrial is enabled, then the AppCache backend in the
 // browser will require origin trial tokens in order to load or store manifests