Fix reverting use of IndexedDB as default cache storage on Chromium

Related issue:
- https://github.com/uBlockOrigin/uBlock-issues/issues/399

The advanced setting `cacheStorageAPI` has been added to allow
a user to force the use of IndexedDB as cache storage. Set to
`IndexedDB` to force use of IndexedDB. Default to `unset`.

src/js/background.js

@@ -43,6 +43,7 @@ const µBlock = (function() { // jshint ignore:line
         autoCommentFilterTemplate: '{{date}} {{origin}}',
         autoUpdateAssetFetchPeriod: 120,
         autoUpdatePeriod: 7,
+        cacheStorageAPI: 'unset',
         cacheStorageCompression: true,
         cacheControlForFirefox1376932: 'no-cache, no-store, must-revalidate',
         debugScriptlets: false,

src/js/cachestorage.js

@@ -48,9 +48,12 @@
     // https://github.com/uBlockOrigin/uBlock-issues/issues/328
     //   Use IndexedDB for Chromium as well, to take advantage of LZ4
     //   compression.
+    // https://github.com/uBlockOrigin/uBlock-issues/issues/399
+    //   Revert Chromium support of IndexedDB, use advanced setting to force
+    //   IndexedDB.
     if (
         vAPI.webextFlavor.soup.has('firefox') === false &&
-        vAPI.webextFlavor.soup.has('chromium') === false
+        µBlock.hiddenSettings.cacheStorageAPI.toLowerCase() !== 'indexeddb'
     ) {
         // In case IndexedDB was used as cache storage, remove it.
         indexedDB.deleteDatabase(STORAGE_NAME);

src/js/storage.js

@@ -186,9 +186,10 @@
     vAPI.localStorage.setItem(
         'immediateHiddenSettings',
         JSON.stringify({
+                  cacheStorageAPI: this.hiddenSettings.cacheStorageAPI,
                disableWebAssembly: this.hiddenSettings.disableWebAssembly,
             suspendTabsUntilReady: this.hiddenSettings.suspendTabsUntilReady,
-            userResourcesLocation: this.hiddenSettings.userResourcesLocation
+            userResourcesLocation: this.hiddenSettings.userResourcesLocation,
         })
     );
 };