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

chrome/browser/value_store/testing_value_store.cc

Index: chrome/browser/value_store/testing_value_store.cc
diff --git a/chrome/browser/value_store/testing_value_store.cc b/chrome/browser/value_store/testing_value_store.cc
index c8d177c55147d5f26d0d2ef15853853dbc36cc4d..f9183ea47054fb61ff1a7d6f42a4a14cafb344ca 100644
--- a/chrome/browser/value_store/testing_value_store.cc
+++ b/chrome/browser/value_store/testing_value_store.cc
@@ -124,6 +124,29 @@ ValueStore::WriteResult TestingValueStore::Clear() {
   return Remove(keys);
 }
 
+bool TestingValueStore::Restore() {
+  ReadResult result = Get();
+  std::string previous_key;
+  while (result->HasError() && result->error().code == CORRUPTION) {

[not at google - send to devlin, 2014/02/14 19:35:56]

How does this class get corrupted storage?

I'm surprised how complex these methods are. I would have thought they're
basically no-ops.

[Devlin, 2014/02/18 23:55:22]

Yeah...this might be overkill.  My basic thought was that I wanted the
TestingValueStore to behave as much as possible like a real value store, so that
if we wanted to instigate corruption for testing reasons, it would still behave
like the other stores.  Not worth it?

[not at google - send to devlin, 2014/02/19 21:25:29]

Not worth it.

[Devlin, 2014/02/19 23:12:28]

Done.

+    if (!result->error().key.get() || *result->error().key == previous_key ||
+        !RestoreKey(*result->error().key)) {
+      Clear();
+      result = Get();
+      break;
+    }
+    previous_key = *result->error().key;
+    result = Get();
+  }
+  return result->HasError() && result->error().code == CORRUPTION;
+}
+
+bool TestingValueStore::RestoreKey(const std::string& key) {
+  ReadResult result = Get(key);
+  if (result->HasError() && result->error().code == CORRUPTION)
+    Remove(key);
+  return Get(key)->HasError();
+}
+
 scoped_ptr<ValueStore::Error> TestingValueStore::TestingError() {
   return make_scoped_ptr(new ValueStore::Error(
       error_code_, kGenericErrorMessage, scoped_ptr<std::string>()));