Adding unit tests for PreviewsOptOutStoreSQL

components/previews/core/previews_opt_out_store_sql.cc

Index: components/previews/core/previews_opt_out_store_sql.cc
diff --git a/components/previews/core/previews_opt_out_store_sql.cc b/components/previews/core/previews_opt_out_store_sql.cc
index 6feb4a16ffa5ed3a4f0d7d8b6cca03d52efae9ee..22ba0a0f5f204b7a227da159756bc478752ddfa3 100644
--- a/components/previews/core/previews_opt_out_store_sql.cc
+++ b/components/previews/core/previews_opt_out_store_sql.cc
@@ -1,49 +1,71 @@
 // 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/previews/core/previews_opt_out_store_sql.h"
 
+#include <string>
+
 #include "base/bind.h"
 #include "base/bind_helpers.h"
+#include "base/command_line.h"
 #include "base/files/file_util.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/sequenced_task_runner.h"
+#include "base/strings/string_number_conversions.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "components/previews/core/previews_black_list.h"
 #include "components/previews/core/previews_black_list_item.h"
 #include "components/previews/core/previews_experiments.h"
 #include "sql/connection.h"
 #include "sql/recovery.h"
 #include "sql/statement.h"
 #include "sql/transaction.h"
 
 namespace previews {
 
 namespace {
 
+// Command line switch to change the previews per row DB size.
+const char kMaxRowsPerHost[] = "previews-max-opt-out-rows-per-host";
+
+// Command line switch to change the previews DB size.
+const char kMaxRows[] = "previews-max-opt-out-rows";
+
+// Returns the maximum number of table rows allowed per host for the previews
+// opt out store. This is enforced during insertion of new navigation entries.
+int MaxRowsPerHostInOptOutDB() {
+  std::string max_rows =
+      base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+          kMaxRowsPerHost);
+  int value;
+  return base::StringToInt(max_rows, &value) ? value : 32;
+}
+
+// Returns the maximum number of table rows allowed for the previews opt out
+// store. This is enforced during load time; thus the database can grow
+// larger than this temporarily.
+int MaxRowsInOptOutDB() {
+  std::string max_rows =
+      base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(kMaxRows);
+  int value;
+  return base::StringToInt(max_rows, &value) ? value : 3200;
+}
+
 // This is a macro instead of a const, so it can be used inline in other SQL
 // statements below.
 #define PREVIEWS_TABLE_NAME "previews_v1"
 
-// The maximum number of entries allowed per host. Entries are evicted based on
-// entry time.
-const int kMaxRowsPerHost = 32;
-
-// The maximum number of entries allowed in the data base. Entries are evicted
-// based on entry time.
-const int kMaxRowsInDB = 3200;
-
 void CreateSchema(sql::Connection* db) {
   const char kSql[] = "CREATE TABLE IF NOT EXISTS " PREVIEWS_TABLE_NAME
                       " (host_name VARCHAR NOT NULL,"
                       " time INTEGER NOT NULL,"
                       " opt_out INTEGER NOT NULL,"
                       " type INTEGER NOT NULL,"
                       " PRIMARY KEY(host_name, time DESC, opt_out, type))";
   if (!db->Execute(kSql))
     return;
 }
@@ -122,34 +144,34 @@ void AddPreviewNavigationToDataBase(sql::Connection* db,
   statement_insert.BindInt64(1, now.ToInternalValue());
   statement_insert.BindBool(2, opt_out);
   statement_insert.BindInt(3, static_cast<int>(type));
   statement_insert.Run();
 }
 
 // Removes entries for |host_name| if the per-host row limit is exceeded.
 // Removes entries if per data base row limit is exceeded.
 void MaybeEvictHostEntryFromDataBase(sql::Connection* db,
                                      const std::string& host_name) {
-  // Delete the oldest entries if there are more than |kMaxRowsPerHost| for
-  // |host_name|.
+  // Delete the oldest entries if there are more than |MaxRowsPerHostInOptOutDB|
+  // for |host_name|.
   // DELETE ... LIMIT -1 OFFSET x means delete all but the first x entries.
   const char kSqlDeleteByHost[] = "DELETE FROM " PREVIEWS_TABLE_NAME
                                   " WHERE ROWID IN"
                                   " (SELECT ROWID from " PREVIEWS_TABLE_NAME
                                   " WHERE host_name == ?"
                                   " ORDER BY time DESC"
                                   " LIMIT -1 OFFSET ?)";
 
   sql::Statement statement_delete_by_host(
       db->GetCachedStatement(SQL_FROM_HERE, kSqlDeleteByHost));
   statement_delete_by_host.BindString(0, host_name);
-  statement_delete_by_host.BindInt(1, kMaxRowsPerHost);
+  statement_delete_by_host.BindInt(1, MaxRowsPerHostInOptOutDB());
   statement_delete_by_host.Run();
 }
 
 void LoadBlackListFromDataBase(
     sql::Connection* db,
     scoped_refptr<base::SingleThreadTaskRunner> runner,
     LoadBlackListCallback callback) {
   // Gets the table sorted by host and time. Limits the number of hosts using
   // most recent opt_out time as the limiting function.
   const char kSql[] =
@@ -173,32 +195,32 @@ void LoadBlackListFromDataBase(
     // Allows the internal logic of PreviewsBlackListItem to determine how to
     // evict entries when there are more than
     // |StoredHistoryLengthForBlackList()| for the host.
     black_list_item->AddPreviewNavigation(
         statement.ColumnBool(2),
         base::Time::FromInternalValue(statement.ColumnInt64(1)));
   }
 
   UMA_HISTOGRAM_COUNTS_10000("Previews.OptOut.DBRowCount", count);
 
-  if (count > kMaxRowsInDB) {
+  if (count > MaxRowsInOptOutDB()) {
     // Delete the oldest entries if there are more than |kMaxEntriesInDB|.
     // DELETE ... LIMIT -1 OFFSET x means delete all but the first x entries.
     const char kSqlDeleteByDBSize[] = "DELETE FROM " PREVIEWS_TABLE_NAME
                                       " WHERE ROWID IN"
                                       " (SELECT ROWID from " PREVIEWS_TABLE_NAME
                                       " ORDER BY time DESC"
                                       " LIMIT -1 OFFSET ?)";
 
     sql::Statement statement_delete(
         db->GetCachedStatement(SQL_FROM_HERE, kSqlDeleteByDBSize));
-    statement_delete.BindInt(0, kMaxRowsInDB);
+    statement_delete.BindInt(0, MaxRowsInOptOutDB());
     statement_delete.Run();
   }
 
   runner->PostTask(FROM_HERE,
                    base::Bind(callback, base::Passed(&black_list_item_map)));
 }
 
 // Synchronous implementations, these are run on the background thread
 // and actually do the work to access the SQL data base.
 void LoadBlackListSync(sql::Connection* db,