Revert of [Sync] Erase sync DB when corrupted

sync/syncable/directory_backing_store_unittest.cc

Index: sync/syncable/directory_backing_store_unittest.cc
diff --git a/sync/syncable/directory_backing_store_unittest.cc b/sync/syncable/directory_backing_store_unittest.cc
index 0cc723fc7ce1e0958bb48f9eb5d5443623dc8dd4..435533c969d409ee3e30468f6667ade1fcb335ab 100644
--- a/sync/syncable/directory_backing_store_unittest.cc
+++ b/sync/syncable/directory_backing_store_unittest.cc
@@ -7,6 +7,8 @@
 #include <string>
 
 #include "base/files/file_path.h"
+#include "base/files/file_util.h"
+#include "base/files/scoped_file.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop/message_loop.h"
@@ -25,7 +27,6 @@
 #include "sync/syncable/directory_backing_store.h"
 #include "sync/syncable/on_disk_directory_backing_store.h"
 #include "sync/syncable/syncable-inl.h"
-#include "sync/test/directory_backing_store_corruption_testing.h"
 #include "sync/test/test_directory_backing_store.h"
 #include "sync/util/time.h"
 #include "testing/gtest/include/gtest/gtest-param-test.h"
@@ -4094,6 +4095,7 @@
   bool was_called = false;
   const base::Closure handler =
       base::Bind(&CatastrophicErrorHandler, &was_called);
+
   // Create a DB with many entries.
   scoped_ptr<OnDiskDirectoryBackingStoreForTest> dbs(
       new OnDiskDirectoryBackingStoreForTest(GetUsername(), GetDatabasePath()));
@@ -4102,19 +4104,32 @@
   ASSERT_TRUE(LoadAndIgnoreReturnedData(dbs.get()));
   ASSERT_FALSE(dbs->DidFailFirstOpenAttempt());
   Directory::SaveChangesSnapshot snapshot;
-  for (int i = 0; i < corruption_testing::kNumEntriesRequiredForCorruption;
-       ++i) {
+  const int num_entries = 4000;
+  for (int i = 0; i < num_entries; ++i) {
     snapshot.dirty_metas.insert(CreateEntry(i).release());
   }
   ASSERT_TRUE(dbs->SaveChanges(snapshot));
-  // Corrupt it.
-  ASSERT_TRUE(corruption_testing::CorruptDatabase(GetDatabasePath()));
+
+  // Corrupt the DB by write a bunch of zeros at the beginning.
+  {
+    // Because the file is already open for writing (see dbs above), it's
+    // important that we open it in a sharing compatible way for platforms that
+    // have the concept of shared/exclusive file access (e.g. Windows).
+    base::ScopedFILE db_file(base::OpenFile(GetDatabasePath(), "wb"));
+    ASSERT_TRUE(db_file.get());
+    const std::string zeros(4096, '\0');
+    ASSERT_EQ(1U, fwrite(zeros.data(), zeros.size(), 1, db_file.get()));
+  }
+
   // Attempt to save all those entries again. See that it fails (because of the
   // corruption).
   //
-  // If this test fails because SaveChanges returned true, it may mean you need
-  // to increase the number of entries written to the DB. See also
-  // |kNumEntriesRequiredForCorruption|.
+  // If this test fails because SaveChanges returned true, it may mean that you
+  // need to increase the number of entries written to the DB. Try increasing
+  // the value of num_entries above. The value needs to be large enough to force
+  // the underlying DB to be read from disk before writing. The value *may*
+  // depend on the underlying DB page size as well as the DB's cache_size
+  // PRAGMA.
   ASSERT_FALSE(dbs->SaveChanges(snapshot));
   // At this point the handler has been posted but not executed.
   ASSERT_FALSE(was_called);