health filesystem: update garbageCollect() function.

Bug: 111655771
Test: run dev gc on vold

Change-Id: I2cef404f9e2720c1be7822895187a590837763c8
diff --git a/health/filesystem/1.0/IGarbageCollectCallback.hal b/health/filesystem/1.0/IGarbageCollectCallback.hal
new file mode 100644
index 0000000..901c35c
--- /dev/null
+++ b/health/filesystem/1.0/IGarbageCollectCallback.hal
@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package android.hardware.health.filesystem@1.0;
+
+/**
+ * Callback interface to IFileSystem.garbageCollect.
+ */
+interface IGarbageCollectCallback {
+    /**
+     * When garbage collection has finished, the implementation must
+     * invoke this function to indicate the result of the garbage collection.
+     *
+     * @return result Execution result. See documentation for Result for
+     *     details.
+     */
+    oneway onFinish(Result result);
+};