Bug 833609 - Part 1: add a manual call to shrink memory usage to Sqlite.jsm. r=mak

toolkit/modules/Sqlite.jsm

@@ -586,6 +586,15 @@ OpenedConnection.prototype = Object.freeze({
     );
   },
 
+  /**
+   * Free up as much memory from the underlying database connection as possible.
+   *
+   * @return Promise<>
+   */
+  shrinkMemory: function () {
+    return this.execute("PRAGMA shrink_memory");
+  },
+
   _executeStatement: function (sql, statement, params, onRow) {
     if (statement.state != statement.MOZ_STORAGE_STATEMENT_READY) {
       throw new Error("Statement is not ready for execution.");

toolkit/modules/tests/xpcshell/test_sqlite.js

@@ -323,3 +323,12 @@ add_task(function test_detect_multiple_transactions() {
   yield c.close();
 });
 
+add_task(function test_shrink_memory() {
+  let c = yield getDummyDatabase("shrink_memory");
+
+  // It's just a simple sanity test. We have no way of measuring whether this
+  // actually does anything.
+
+  yield c.shrinkMemory();
+  yield c.close();
+});