Remove overeager DCHECK in SnapshotController.

components/offline_pages/snapshot_controller_unittest.cc

 // Copyright 2016 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 "components/offline_pages/snapshot_controller.h"
 
 #include "base/bind.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/test/test_mock_time_task_runner.h"
@@ skipping 143 matching lines @@
   EXPECT_EQ(1, snapshot_count());
 
   controller()->Reset();
   controller()->DocumentAvailableInMainFrame();
   FastForwardBy(base::TimeDelta::FromMilliseconds(
       controller()->GetDelayAfterDocumentAvailableForTest()));
   // No snapshot since session was reset.
   EXPECT_EQ(2, snapshot_count());
 }
 
+// This simulated a Reset while there is ongoing snapshot, which is reported
+// as done later. That reporting should have no effect nor crash.
+TEST_F(SnapshotControllerTest, ClientResetWhileSnapshotting) {
+  controller()->DocumentOnLoadCompletedInMainFrame();
+  EXPECT_EQ(1, snapshot_count());
+  // This normally happens when navigation starts.
+  controller()->Reset();
+  controller()->PendingSnapshotCompleted();
+  // Next snapshot should be initiated when new document is loaded.
+  controller()->DocumentAvailableInMainFrame();
+  FastForwardBy(base::TimeDelta::FromMilliseconds(
+      controller()->GetDelayAfterDocumentAvailableForTest()));
+  // No snapshot since session was reset.
+  EXPECT_EQ(2, snapshot_count());
+}
+
 }  // namespace offline_pages