Add trace to the caller of QuotaManager::GetAvailableSpace

storage/browser/quota/quota_callbacks.h

Index: storage/browser/quota/quota_callbacks.h
diff --git a/storage/browser/quota/quota_callbacks.h b/storage/browser/quota/quota_callbacks.h
index 36bca1e5c4dd8a94d35c0ee82832967abc7dfd76..4746c5ee14c9428a82d43f366e703be08a8ed354 100644
--- a/storage/browser/quota/quota_callbacks.h
+++ b/storage/browser/quota/quota_callbacks.h
@@ -60,6 +60,10 @@ class CallbackQueue {
     callbacks_.swap(other->callbacks_);
   }
 
+  size_t size() const {
+    return callbacks_.size();
+  }
+
  private:
   std::vector<CallbackType> callbacks_;
 };