Notify GCMAppHandlers when the store is reset, so they clear cached IDs

components/gcm_driver/gcm_client_impl.cc

Index: components/gcm_driver/gcm_client_impl.cc
diff --git a/components/gcm_driver/gcm_client_impl.cc b/components/gcm_driver/gcm_client_impl.cc
index 080a7d006fb208bdbcff659566dec87c476f049b..f4211dbfd55158abb9fa370dcb674f377379cc45 100644
--- a/components/gcm_driver/gcm_client_impl.cc
+++ b/components/gcm_driver/gcm_client_impl.cc
@@ -812,6 +812,8 @@ void GCMClientImpl::DestroyStoreCallback(bool success) {
 }
 
 void GCMClientImpl::ResetStoreCallback(bool success) {
+  delegate_->OnStoreReset();

[jianli, 2016/11/08 23:54:57]

Do we want to call OnStoreReset if |success| is false?

[johnme, 2016/11/09 19:33:48]

Yes, I think so. Looking at the source code of leveldb::DestroyDB, it can return
a non-OK success if it deletes some of the DB files but (due to I/O errors)
fails to delete all of them. In such cases the store will have suffered
sufficient dataloss that it is unlikely to be recoverable (on top of whatever
corruption triggered the attempted reset).

And if one of the successfully deleted files is the "CURRENT" file, then
GCMStoreImpl's DatabaseExists function will in fact consider the DB to no longer
exist (to avoid https://crbug.com/650254), and hence the next
GCMClientImpl::OnLoadCompleted will simply call
Load(GCMStore::CREATE_IF_MISSING, ...) to create a new store rather than calling
ResetStore (so in such cases the partial reset is the last chance to fire an
OnStoreReset event).

In the unlikely event that the GCM Store completely fails to be reset (e.g.
because leveldb::DestroyDB fails to obtain a lock) and turns out to be
recoverable, there's little harm from having app handlers unnecessarily cleared
their state - they'll just re-register in due course (and may even end up
getting the same registration id).

[jianli, 2016/11/09 21:54:23]

Please add some comments to explain this.

[johnme, 2016/11/10 19:56:54]

Done.

+
   if (!success) {
     LOG(ERROR) << "Failed to reset GCM store";
     RecordResetStoreErrorToUMA(DESTROYING_STORE_FAILED);