Method to determine isolated storage mode.

Mostly designed for use by tests, but start using it elsewhere in OS
for consistency.

Bug: 119713234
Test: manual
Change-Id: I803671fd84547b75337bebf00c2fa2bdaf0f72e7
diff --git a/services/core/java/com/android/server/AppOpsService.java b/services/core/java/com/android/server/AppOpsService.java
index 356a4da..8d912fa 100644
--- a/services/core/java/com/android/server/AppOpsService.java
+++ b/services/core/java/com/android/server/AppOpsService.java
@@ -692,7 +692,7 @@
                     }
                 });
 
-        if (!SystemProperties.getBoolean(StorageManager.PROP_ISOLATED_STORAGE, false)) {
+        if (!StorageManager.hasIsolatedStorage()) {
             StorageManagerInternal storageManagerInternal = LocalServices.getService(
                     StorageManagerInternal.class);
             storageManagerInternal.addExternalStoragePolicy(