[Ext Registry] Do not try to re-watch registry if we are already watching it.

chrome/browser/extensions/external_registry_loader_win_unittest.cc

+// Copyright 2017 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 "chrome/browser/extensions/external_registry_loader_win.h"
+
+#include "base/compiler_specific.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/run_loop.h"
+#include "content/public/test/test_browser_thread_bundle.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace extensions {
+
+namespace {
+
+class TestExternalRegistryLoader : public ExternalRegistryLoader {
+ public:
+  TestExternalRegistryLoader() {}
+
+  using ExternalRegistryLoader::StartLoading;
+
+  void WaitForTwoLoadsToFinished() {
+    // Run() returns immediately if Quit() has already been called.
+    run_loop_.Run();
+  }
+
+ private:
+  ~TestExternalRegistryLoader() override {}
+
+  void LoadFinished() {
+    ExternalRegistryLoader::LoadFinished();
+    ++load_finished_count_;
+    if (load_finished_count_ == 2)
+      run_loop_.Quit();
+  }
+
+  base::RunLoop run_loop_;
+  int load_finished_count_ = 0;
+
+  DISALLOW_COPY_AND_ASSIGN(TestExternalRegistryLoader);
+};
+
+}  // namespace
+
+class ExternalRegistryLoaderUnittest : public testing::Test {
+ public:
+  ExternalRegistryLoaderUnittest()
+      : thread_bundle_(content::TestBrowserThreadBundle::IO_MAINLOOP) {}
+  ~ExternalRegistryLoaderUnittest() override {}
+
+ private:
+  content::TestBrowserThreadBundle thread_bundle_;
+
+  DISALLOW_COPY_AND_ASSIGN(ExternalRegistryLoaderUnittest);
+};
+
+// Tests that calling StartLoading() more than once doesn't fail DCHECK.
+// Regression test for https://crbug.com/653045.
+TEST_F(ExternalRegistryLoaderUnittest, TwoStartLoadingDoesNotCrash) {
+  scoped_refptr<TestExternalRegistryLoader> test_loader =
+      make_scoped_refptr(new TestExternalRegistryLoader());
+
+  test_loader->StartLoading();
+  test_loader->StartLoading();
+
+  test_loader->WaitForTwoLoadsToFinished();
+  // Let registry watcher code complete.
+  base::RunLoop().RunUntilIdle();
+}
+
+}  // namespace extensions