Protect against |main_window_| being null.

content/shell/browser/layout_test/blink_test_controller.cc

 // Copyright 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/shell/browser/layout_test/blink_test_controller.h"
 
 #include <stddef.h>
 
 #include <iostream>
 #include <set>
@@ skipping 703 matching lines @@
       ShellContentBrowserClient::Get()->browser_context();
   StoragePartition* storage_partition =
       BrowserContext::GetStoragePartition(browser_context, nullptr);
   storage_partition->GetServiceWorkerContext()->ClearAllServiceWorkersForTest(
       base::Bind(&BlinkTestController::OnAllServiceWorkersCleared,
                  base::Unretained(this)));
   storage_partition->ClearBluetoothAllowedDevicesMapForTesting();
 }
 
 void BlinkTestController::OnAllServiceWorkersCleared() {
-  Send(new ShellViewMsg_Reset(
-      main_window_->web_contents()->GetRenderViewHost()->GetRoutingID()));
+  if (main_window_) {
+    Send(new ShellViewMsg_Reset(
+        main_window_->web_contents()->GetRenderViewHost()->GetRoutingID()));
+  }
 }
 
 void BlinkTestController::OnImageDump(const std::string& actual_pixel_hash,
                                       const SkBitmap& image) {
   printer_->PrintImageHeader(actual_pixel_hash, expected_pixel_hash_);
 
   // Only encode and dump the png if the hashes don't match. Encoding the
   // image is really expensive.
   if (actual_pixel_hash != expected_pixel_hash_) {
     std::vector<unsigned char> png;
@@ skipping 303 matching lines @@
   }
   DCHECK(layout_test_control_map_[frame].get());
   return layout_test_control_map_[frame].get();
 }
 
 void BlinkTestController::HandleLayoutTestControlError(RenderFrameHost* frame) {
   layout_test_control_map_.erase(frame);
 }
 
 }  // namespace content