[IndexedDB] Adding transaction and value support to observers

content/browser/indexed_db/indexed_db_transaction_coordinator.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/indexed_db/indexed_db_transaction_coordinator.h"
 
 #include "base/logging.h"
 #include "content/browser/indexed_db/indexed_db_transaction.h"
 #include "third_party/WebKit/public/platform/modules/indexeddb/WebIDBTypes.h"
 
 namespace content {
 
 IndexedDBTransactionCoordinator::IndexedDBTransactionCoordinator() {}
 
 IndexedDBTransactionCoordinator::~IndexedDBTransactionCoordinator() {
   DCHECK(queued_transactions_.empty());
   DCHECK(started_transactions_.empty());
 }
 
 void IndexedDBTransactionCoordinator::DidCreateTransaction(
     IndexedDBTransaction* transaction) {
   DCHECK(!queued_transactions_.count(transaction));
   DCHECK(!started_transactions_.count(transaction));
   DCHECK_EQ(IndexedDBTransaction::CREATED, transaction->state());
 
   queued_transactions_.insert(transaction);
   ProcessQueuedTransactions();
 }
 
+void IndexedDBTransactionCoordinator::DidCreateObserverTransaction(

[jsbell, 2017/01/13 00:14:12]

Maybe comment here that observer txs jump to the head of the queue?

[dmurph, 2017/01/13 01:50:43]

Done.

+    IndexedDBTransaction* transaction) {
+  DCHECK(!queued_transactions_.count(transaction));
+  DCHECK(!started_transactions_.count(transaction));
+  DCHECK_EQ(IndexedDBTransaction::CREATED, transaction->state());
+
+  started_transactions_.insert_front(transaction);
+  ProcessQueuedTransactions();
+}
+
 void IndexedDBTransactionCoordinator::DidFinishTransaction(
     IndexedDBTransaction* transaction) {
   if (queued_transactions_.count(transaction)) {
     DCHECK(!started_transactions_.count(transaction));
     queued_transactions_.erase(transaction);
   } else {
     DCHECK(started_transactions_.count(transaction));
     started_transactions_.erase(transaction);
   }
 
@@ skipping 105 matching lines @@
 
     case blink::WebIDBTransactionModeReadOnly:
     case blink::WebIDBTransactionModeReadWrite:
       return !DoSetsIntersect(transaction->scope(), locked_scope);
   }
   NOTREACHED();
   return false;
 }
 
 }  // namespace content