Add a Restore() method to ValueStore and make StorageAPI use it

chrome/browser/extensions/api/storage/storage_api.h

Index: chrome/browser/extensions/api/storage/storage_api.h
diff --git a/chrome/browser/extensions/api/storage/storage_api.h b/chrome/browser/extensions/api/storage/storage_api.h
index a37ae6dbeed241edd5597adb72705aa5e6e36586..0a1fa50712482325199d657d544ab6b4a55a2517 100644
--- a/chrome/browser/extensions/api/storage/storage_api.h
+++ b/chrome/browser/extensions/api/storage/storage_api.h
@@ -30,24 +30,43 @@ class SettingsFunction : public ChromeAsyncExtensionFunction {
   // may return false to imply failure.
   virtual bool RunWithStorage(ValueStore* storage) = 0;
 
-  // Sets error_ or result_ depending on the value of a storage ReadResult, and
-  // returns whether the result implies success (i.e. !error).
-  bool UseReadResult(ValueStore::ReadResult result);
-
-  // Sets error_ depending on the value of a storage WriteResult, sends a
-  // change notification if needed, and returns whether the result implies
-  // success (i.e. !error).
-  bool UseWriteResult(ValueStore::WriteResult result);
+  // Handles the |result| of a read function.
+  // - If the result succeeded, this will set |result_| and return.
+  // - If |result| failed with a ValueStore::CORRUPTION error, this will call
+  //   RestoreStorageAndRetry(), and return that result.
+  // - If the |result| failed with a different error, this will set |error_|
+  //   and return.
+  bool UseReadResult(ValueStore::ReadResult result, ValueStore* storage);
+
+  // Handles the |result| of a write function.
+  // - If the result succeeded, this will set |result_| and return.
+  // - If |result| failed with a ValueStore::CORRUPTION error, this will call
+  //   RestoreStorageAndRetry(), and return that result.
+  // - If the |result| failed with a different error, this will set |error_|
+  //   and return.
+  // This will also send out a change notification, if appropriate.
+  bool UseWriteResult(ValueStore::WriteResult result, ValueStore* storage);
 
  private:
   // Called via PostTask from RunImpl.  Calls RunWithStorage and then
   // SendResponse with its success value.
   void AsyncRunWithStorage(ValueStore* storage);
 
+  // Called if we encounter a ValueStore::CORRUPTION error. Tries to restore
+  // the ValueStore and re-run the API function. If the storage cannot be
+  // restored, then sets error and returns. This also sets
+  // the |tried_restoring_storage_| flag to ensure we don't enter a loop.
+  bool RestoreStorageAndRetry(const ValueStore::Error& error,
+                              ValueStore* storage);
+
   // The settings namespace the call was for.  For example, SYNC if the API
   // call was chrome.settings.experimental.sync..., LOCAL if .local, etc.
   settings_namespace::Namespace settings_namespace_;
 
+  // A flag indicating whether or not we have tried to restore storage. We
+  // should only ever try once (per API call) in order to avoid entering a loop.
+  bool tried_restoring_storage_;
+
   // Observers, cached so that it's only grabbed from the UI thread.
   scoped_refptr<SettingsObserverList> observers_;
 };