[WIP] histroy: Adjust cache size OnMemoryStateChange()

sql/connection.h

 // 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.
 
 #ifndef SQL_CONNECTION_H_
 #define SQL_CONNECTION_H_
 
 #include <stddef.h>
 #include <stdint.h>
 #include <map>
@@ skipping 270 matching lines @@
   // if the data isn't actually used soon then preloading just slows down
   // everything else.
   void Preload();
 
   // Try to trim the cache memory used by the database.  If |aggressively| is
   // true, this function will try to free all of the cache memory it can. If
   // |aggressively| is false, this function will try to cut cache memory
   // usage by half.
   void TrimMemory(bool aggressively);
 
+  // Update the cache size. Unlike set_cache_size(), this will have an effect
+  // even after initialization.  Returns true if cache size is successfully
+  // updated.  The total cache size in bytes will be page_size * new_cache_size.
+  bool UpdateCacheSize(int new_cache_size);

[Scott Hess - ex-Googler, 2016/09/01 18:29:09]

I want to complain that this should be called Set rather than Update, but, sigh,
set_cache_size() would be confusing.

Maybe it should be SetCacheSize(), and if the database was not open yet it would
set cache_size_ and exit, but if the database was open it would also issue the
pragma.

[Maybe the pre-init configuration should really be pushed to a
Connection::Config object passed to the constructor.  I'll think about that.]

+
   // Raze the database to the ground.  This approximates creating a
   // fresh database from scratch, within the constraints of SQLite's
   // locking protocol (locks and open handles can make doing this with
   // filesystem operations problematic).  Returns true if the database
   // was razed.
   //
   // false is returned if the database is locked by some other
   // process.  RazeWithTimeout() may be used if appropriate.
   //
   // NOTE(shess): Raze() will DCHECK in the following situations:
@@ skipping 500 matching lines @@
 
   // Stores the dump provider object when db is open.
   std::unique_ptr<ConnectionMemoryDumpProvider> memory_dump_provider_;
 
   DISALLOW_COPY_AND_ASSIGN(Connection);
 };
 
 }  // namespace sql
 
 #endif  // SQL_CONNECTION_H_