[sql] Refactor to remove use of const_cast<>.

sql/connection.h

Index: sql/connection.h
diff --git a/sql/connection.h b/sql/connection.h
index 1e3414f40ca72912b0b8e0b64af1fa37d5e78a1f..c51a28ca14596b5d3d36ea45bc7a555d5aa69436 100644
--- a/sql/connection.h
+++ b/sql/connection.h
@@ -339,6 +339,7 @@ class SQL_EXPORT Connection {
    public:
     // Default constructor initializes to an invalid statement.
     StatementRef();
+    explicit StatementRef(sqlite3_stmt* stmt);
     StatementRef(Connection* connection, sqlite3_stmt* stmt);
 
     // When true, the statement can be used.
@@ -388,6 +389,14 @@ class SQL_EXPORT Connection {
   bool ExecuteWithTimeout(const char* sql, base::TimeDelta ms_timeout)
       WARN_UNUSED_RESULT;
 
+  // Internal helper for const functions.  Like GetUniqueStatement(),
+  // except the statement is not entered into open_statements_,
+  // allowing this function to be const.  Open statements can block
+  // closing the database, so only use in cases where the last ref is
+  // released before close could be called (which should always be the
+  // case for const functions).
+  scoped_refptr<StatementRef> GetUntrackedStatement(const char* sql) const;
+
   // The actual sqlite database. Will be NULL before Init has been called or if
   // Init resulted in an error.
   sqlite3* db_;