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..ee93a21a15d673e8019783bc01791df4c2c30076 100644
--- a/components/previews/core/previews_opt_out_store_sql.cc
+++ b/components/previews/core/previews_opt_out_store_sql.cc
@@ -1,49 +1,70 @@
 // 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.

[tbansal1, 2016/11/07 17:10:26]

May be add a comment that says that the limit is enforced at the time of preview
insertion.

[RyanSturm, 2016/11/07 18:24:28]

Done.

+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.

[tbansal1, 2016/11/07 17:10:26]

Can you add a comment that says that the limit is enforced when the database is
loaded next time, so it is possible for the database to temporarily grow beyond
this size. This is important because this is currently a bit unintuitive.

[RyanSturm, 2016/11/07 18:24:28]

Done.

+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 +143,34 @@ 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 +194,32 @@ 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,