Revert of [sql] Use memory-mapped I/O for sql::Connection.

sql/connection.h

Index: sql/connection.h
diff --git a/sql/connection.h b/sql/connection.h
index d456b6cd88c9627b488c970dcd46de4a72c7945a..19592d9f0e44ed68764b9d25a88d9a65424ba9b7 100644
--- a/sql/connection.h
+++ b/sql/connection.h
@@ -146,9 +146,6 @@
   // other platforms.
   void set_restrict_to_user() { restrict_to_user_ = true; }
 
-  // Call to opt out of memory-mapped file I/O.
-  void set_mmap_disabled() { mmap_disabled_ = true; }
-
   // Set an error-handling callback.  On errors, the error number (and
   // statement, if available) will be passed to the callback.
   //
@@ -641,12 +638,6 @@
     return clock_->Now();
   }
 
-  // Release page-cache memory if memory-mapped I/O is enabled and the database
-  // was changed.  Passing true for |implicit_change_performed| allows
-  // overriding the change detection for cases like DDL (CREATE, DROP, etc),
-  // which do not participate in the total-rows-changed tracking.
-  void ReleaseCacheMemoryIfNeeded(bool implicit_change_performed);
-
   // The actual sqlite database. Will be NULL before Init has been called or if
   // Init resulted in an error.
   sqlite3* db_;
@@ -688,17 +679,6 @@
   // databases.
   bool poisoned_;
 
-  // |true| if SQLite memory-mapped I/O is not desired for this connection.
-  bool mmap_disabled_;
-
-  // |true| if SQLite memory-mapped I/O was enabled for this connection.
-  // Used by ReleaseCacheMemoryIfNeeded().
-  bool mmap_enabled_;
-
-  // Used by ReleaseCacheMemoryIfNeeded() to track if new changes have happened
-  // since memory was last released.
-  int total_changes_at_last_release_;
-
   ErrorCallback error_callback_;
 
   // Tag for auxiliary histograms.