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

chrome/browser/value_store/value_store.h

Index: chrome/browser/value_store/value_store.h
diff --git a/chrome/browser/value_store/value_store.h b/chrome/browser/value_store/value_store.h
index 2b203ea57b779297a647e991b0825b64e64de9ae..d1ca17773560f484da5ba9690cdd55d6d514d957 100644
--- a/chrome/browser/value_store/value_store.h
+++ b/chrome/browser/value_store/value_store.h
@@ -77,6 +77,10 @@ class ValueStore {
 
     bool HasError() const { return error_; }
 
+    bool IsCorrupted() const {
+      return error_.get() && error_->code == CORRUPTION;
+    }
+
     // Gets the settings read from the storage. Note that this represents
     // the root object. If you request the value for key "foo", that value will
     // be in |settings|.|foo|.
@@ -191,6 +195,27 @@ class ValueStore {
 
   // Clears the storage.
   virtual WriteResult Clear() = 0;
+
+  // In the event of corruption, the ValueStore should be able to restore
+  // itself. This means deleting local corrupted files. If only a few keys are
+  // corrupted, then some of the database may be saved. If the full database is
+  // corrupted, this will erase it in its entirety.
+  // Returns true on success, false on failure. The only way this will fail is
+  // if we also cannot delete the database file.
+  // Note: This method needs to read (and possibly delete) the whole database,
+  // so it is slow and should be used sparingly.
+  // Note: This method (and the following RestoreKey()) are rude, and do not
+  // make any logs, track changes, or other generally polite things. Please do
+  // not use these as substitutes for Clear() and Remove().
+  virtual bool Restore() = 0;
+
+  // Similar to Restore(), but for only a particular key. If the key is corrupt,
+  // this will forcefully remove the key. It does not look at the database on
+  // the whole, which makes it faster, but does not guarantee there is no
+  // additional corruption.
+  // Returns true on success, and false on failure. If false, the next step is
+  // probably to Restore() the whole database.
+  virtual bool RestoreKey(const std::string& key) = 0;
 };
 
 #endif  // CHROME_BROWSER_VALUE_STORE_VALUE_STORE_H_