Use a scoped_refptr in the IndexedDBCallbacks constructor.

Follow-up to r433964 to change IndexedDBCallbacks to take its
IndexedDBDispatcherHost argument as a scoped_refptr as suggested by
dcheng@.

BUG=None

Review-Url: https://codereview.chromium.org/2521903004
Cr-Commit-Position: refs/heads/master@{#434822}

content/browser/indexed_db/indexed_db_callbacks.cc

@@ -140,10 +140,10 @@ class IndexedDBCallbacks::IOThreadHelper {
 };
 
 IndexedDBCallbacks::IndexedDBCallbacks(
-    IndexedDBDispatcherHost* dispatcher_host,
+    scoped_refptr<IndexedDBDispatcherHost> dispatcher_host,
     const url::Origin& origin,
     ::indexed_db::mojom::CallbacksAssociatedPtrInfo callbacks_info)
-    : dispatcher_host_(dispatcher_host),
+    : dispatcher_host_(std::move(dispatcher_host)),
       host_transaction_id_(kNoTransaction),
       origin_(origin),
       data_loss_(blink::WebIDBDataLossNone),

content/browser/indexed_db/indexed_db_callbacks.h

@@ -37,7 +37,7 @@ class CONTENT_EXPORT IndexedDBCallbacks
     : public base::RefCounted<IndexedDBCallbacks> {
  public:
   IndexedDBCallbacks(
-      IndexedDBDispatcherHost* dispatcher_host,
+      scoped_refptr<IndexedDBDispatcherHost> dispatcher_host,
       const url::Origin& origin,
       ::indexed_db::mojom::CallbacksAssociatedPtrInfo callbacks_info);