Add 'fstrim' command for use from shell.

Test: builds, boots, new command works
Bug: 20948199
Change-Id: If7b122a6c98a4ce2a2f38e545015a22decd1b516
diff --git a/core/java/android/os/storage/IStorageManager.aidl b/core/java/android/os/storage/IStorageManager.aidl
index 98cbce6..27c0526 100644
--- a/core/java/android/os/storage/IStorageManager.aidl
+++ b/core/java/android/os/storage/IStorageManager.aidl
@@ -288,4 +288,5 @@
     ParcelFileDescriptor mountAppFuse(in String name) = 69;
     void addUserKeyAuth(int userId, int serialNumber, in byte[] token, in byte[] secret) = 70;
     void fixateNewestUserKeyAuth(int userId) = 71;
-}
\ No newline at end of file
+    void fstrim(int flags) = 72;
+}