Not creating ClientUsageTracker for unsupported storage type.

webkit/browser/quota/usage_tracker.cc

Index: webkit/browser/quota/usage_tracker.cc
diff --git a/webkit/browser/quota/usage_tracker.cc b/webkit/browser/quota/usage_tracker.cc
index 4bf64880c3caa2db1b89d8c872ee73d17acbcf6e..57b5e0d24eacd11c9eb7670928deedfe6d5f6f2e 100644
--- a/webkit/browser/quota/usage_tracker.cc
+++ b/webkit/browser/quota/usage_tracker.cc
@@ -78,8 +78,10 @@ UsageTracker::UsageTracker(const QuotaClientList& clients,
   for (QuotaClientList::const_iterator iter = clients.begin();
       iter != clients.end();
       ++iter) {
-    client_tracker_map_[(*iter)->id()] =
-        new ClientUsageTracker(this, *iter, type, special_storage_policy);
+    if ((*iter)->DoesSupport(type)) {

[michaeln, 2013/08/28 19:46:05]

Thinning out the size of this map looks great.

I'm curious as to what goes wrong exactly when the set is not pruned in this
way? Is there another code change that could/should be made in addition to
thinning out the set?

[SeRya, 2013/08/29 09:07:26]

if you query
quota_manager->GetUsageTracker(kSyncableStorageType)->GetClientTracker(kFilesystem)->GetHostUsage(...)

it fails in method GetFileSystemBackend if syncable backend is not registered
(it happens in tests).

Stack is:
fileapi::FileSystemContext::GetFileSystemBackend()
fileapi::FileSystemContext::GetQuotaUtil()
fileapi::(anonymous namespace)::GetOriginsForHostOnFileThread()
base::internal::RunnableAdapter<>::Run()

It seems that all pieces of code using GetFileSystemBackend expect it may return
NULL so alternatively the following line could be removed from
GetFileSystemBackend:

NOTREACHED() << "Unknown filesystem type: " << type;

In addition to thinning out the set methods UsageTracker::UpdateUsageCache and
UsageTracker::SetUsageCacheEnabled could check result of GetClientTracker for
NULL. This methods calls are indirectly initiated by QuotaClient's what
understand that storage types they support so a tracker always exist for the
type they pass. This check looks unnecessary.

+      client_tracker_map_[(*iter)->id()] =
+          new ClientUsageTracker(this, *iter, type, special_storage_policy);
+    }
   }
 }