Remove unused SQLLite tables from WebData

components/webdata/common/web_database.cc

 // Copyright (c) 2012 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/webdata/common/web_database.h"
 
 #include <algorithm>
 
 #include "base/stl_util.h"
 #include "sql/statement.h"
 #include "sql/transaction.h"
 
 // Current version number.  Note: when changing the current version number,
 // corresponding changes must happen in the unit tests, and new migration test
 // added.  See |WebDatabaseMigrationTest::kCurrentTestedVersionNumber|.
 // static
-const int WebDatabase::kCurrentVersionNumber = 57;
+const int WebDatabase::kCurrentVersionNumber = 58;
 
 namespace {
 
-const int kCompatibleVersionNumber = 57;
+const int kCompatibleVersionNumber = 58;
 
 // Change the version number and possibly the compatibility version of
 // |meta_table_|.
 void ChangeVersion(sql::MetaTable* meta_table,
                    int version_num,
                    bool update_compatible_version_num) {
   meta_table->SetVersionNumber(version_num);
   if (update_compatible_version_num) {
     meta_table->SetCompatibleVersionNumber(
           std::min(version_num, kCompatibleVersionNumber));
@@ skipping 116 matching lines @@
     // erase all their prefs and start over, etc.).
     LOG(WARNING) << "Web database version " << current_version
                  << " is too old to handle.";
     NOTREACHED();
     return sql::INIT_FAILURE;
   }
 
   for (int next_version = current_version + 1;
        next_version <= kCurrentVersionNumber;
        ++next_version) {
+
+    // Do any database-wide migrations.
+    bool update_compatible_version = false;
+    if (!MigrateToVersion(next_version, &update_compatible_version))
+      return FailedMigrationTo(next_version);
+
+    ChangeVersion(&meta_table_, next_version, update_compatible_version);
+
     // Give each table a chance to migrate to this version.
     for (TableMap::iterator it = tables_.begin(); it != tables_.end(); ++it) {
       // Any of the tables may set this to true, but by default it is false.
-      bool update_compatible_version = false;
+      update_compatible_version = false;
       if (!it->second->MigrateToVersion(next_version,
                                         &update_compatible_version)) {
         return FailedMigrationTo(next_version);
       }
 
       ChangeVersion(&meta_table_, next_version, update_compatible_version);
     }
   }
   return sql::INIT_OK;
 }
+
+bool WebDatabase::MigrateToVersion(int version,
+                      bool* update_compatible_version) {
+  // Migrate if necessary.
+  switch (version) {
+    case 58:
+      *update_compatible_version = true;
+      return MigrateToVersion58DropWebAppsAndIntents();
+  }
+
+  return true;
+}
+
+bool WebDatabase::MigrateToVersion58DropWebAppsAndIntents() {
+  sql::Transaction transaction(&db_);
+  return transaction.Begin() &&
+      (!db_.DoesTableExist("web_apps") ||
+        db_.Execute("DROP TABLE web_apps")) &&

[Scott Hess - ex-Googler, 2014/07/10 01:55:53]

This and the others should be like:
  db_.Execute("DROP TABLE IF EXISTS web_apps") &&
rather than manually testing.

[Cait (Slow), 2014/07/14 23:09:45]

Done.

+      (!db_.DoesTableExist("web_app_icons") ||
+        db_.Execute("DROP TABLE web_app_icons")) &&
+      (!db_.DoesTableExist("web_intents") ||
+        db_.Execute("DROP TABLE web_intents")) &&
+      (!db_.DoesTableExist("web_intents_defaults") ||
+        db_.Execute("DROP TABLE web_intents_defaults")) &&
+      transaction.Commit();
+}