Add sm set-isolated-storage [true|false]

Bug: 119038726
Test: manual
Change-Id: I29eeec7872584f1173e9b6d31434b36487515d9e
diff --git a/core/java/android/os/Environment.java b/core/java/android/os/Environment.java
index 0c4a0b3e..1bae3f7 100644
--- a/core/java/android/os/Environment.java
+++ b/core/java/android/os/Environment.java
@@ -468,6 +468,14 @@
     }
 
     /**
+     * Returns location of packages cache directory.
+     * {@hide}
+     */
+    public static File getPackageCacheDirectory() {
+        return new File(getDataSystemDirectory(), "package_cache");
+    }
+
+    /**
      * Return the primary shared/external storage directory. This directory may
      * not currently be accessible if it has been mounted by the user on their
      * computer, has been removed from the device, or some other problem has