Quota: remove unused member from ClientUsageTracker

Change-Id: I3a09a2b8d2fabacbb625e7029e97121a83a03250
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504217
Commit-Queue: Jarryd Goodman <jarrydg@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637844}

storage/browser/quota/client_usage_tracker.cc

@@ -63,15 +63,13 @@ ClientUsageTracker::ClientUsageTracker(
     blink::mojom::StorageType type,
     SpecialStoragePolicy* special_storage_policy,
     StorageMonitor* storage_monitor)
-    : tracker_(tracker),
-      client_(client),
+    : client_(client),
       type_(type),
       storage_monitor_(storage_monitor),
       global_limited_usage_(0),
       global_unlimited_usage_(0),
       global_usage_retrieved_(false),
       special_storage_policy_(special_storage_policy) {
-  DCHECK(tracker_);
   DCHECK(client_);
   if (special_storage_policy_.get())
     special_storage_policy_->AddObserver(this);

storage/browser/quota/client_usage_tracker.h

@@ -104,7 +104,6 @@ class ClientUsageTracker : public SpecialStoragePolicy::Observer,
 
   bool IsStorageUnlimited(const url::Origin& origin) const;
 
-  const UsageTracker* const tracker_;
   QuotaClient* client_;
   const blink::mojom::StorageType type_;
   StorageMonitor* storage_monitor_;