Purge browser cache for dom storage in a smarter way

content/browser/dom_storage/dom_storage_database.cc

 // Copyright 2013 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 "content/browser/dom_storage/dom_storage_database.h"
 
 #include "base/bind.h"
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "sql/statement.h"
@@ skipping 110 matching lines @@
     if (statement.Step())
       known_to_be_empty_ = statement.ColumnInt(0) == 0;
   }
 
   bool success = transaction.Commit();
   if (!success)
     known_to_be_empty_ = old_known_to_be_empty;
   return success;
 }
 
+void DOMStorageDatabase::TrimDatabase() {
+  // We hit this case only on aggressive purging.
+  db_->TrimMemory(true /* aggressively */);

[michaeln, 2016/05/09 21:50:31]

This needs to have a test for IsOpen() or an assertion that it's only called
when IsOpen().

If we do decide to do this unconditionally on each read/write, the ReadAll and
Commit methods could call db_->TrimMem() directly w/o exposing this as a public
method.

[ssid, 2016/05/10 02:04:16]

Fixed.
Sorry I do not understand how do i get the pointer to sql::Connection from
DOMStorageArea. It only holds an object of DOMStorageDatabaseAdapter.
I would have to write:
reinterpret_cast<DOMStorageDatabase*>(backing_.get())->db_->TrimMemory(false);

And also add DOMStorageArea as friend of DOMStorageDatabase.

Am I missing something here?

+}
+
 bool DOMStorageDatabase::LazyOpen(bool create_if_needed) {
   if (failed_to_open_) {
     // Don't try to open a database that we know has failed
     // already.
     return false;
   }
 
   if (IsOpen())
     return true;
 
@@ skipping 147 matching lines @@
       CreateTableV2() &&
       CommitChanges(false, values) &&
       migration.Commit();
 }
 
 void DOMStorageDatabase::Close() {
   db_.reset(NULL);
 }
 
 }  // namespace content