[Sync] Erase sync DB when corrupted

sync/test/directory_backing_store_corruption_testing.h

Index: sync/test/directory_backing_store_corruption_testing.h
diff --git a/sync/test/directory_backing_store_corruption_testing.h b/sync/test/directory_backing_store_corruption_testing.h
new file mode 100644
index 0000000000000000000000000000000000000000..5897ec0466d28d072ffdbb774e7120a010af3155
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+++ b/sync/test/directory_backing_store_corruption_testing.h
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+// Copyright 2015 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.
+
+#ifndef SYNC_TEST_DIRECTORY_BACKING_STORE_CORRUPTION_TESTING_H_
+#define SYNC_TEST_DIRECTORY_BACKING_STORE_CORRUPTION_TESTING_H_
+
+#include "base/files/file_path.h"
+
+namespace syncer {
+namespace syncable {
+namespace corruption_testing {
+
+// The number of DB entries required to reliably trigger detectable corruption
+// using |CorruptDatabase|.
+extern const int kNumEntriesRequiredForCorruption;
+
+// Corrupt the sync database at |backing_file_path|.
+//
+// Returns true if the database was successfully corrupted.
+bool CorruptDatabase(const base::FilePath& backing_file_path);
+
+}  // namespace corruption_util
+}  // namespace syncable
+}  // namespace syncer
+
+#endif  // SYNC_TEST_DIRECTORY_BACKING_STORE_CORRUPTION_TESTING_H_