Rename UserId to UserHandle.

This is the start of turning this into a formal public API.

Change-Id: I5786d2c320f1de41a06ed5d0f65adb68967287a0
diff --git a/core/java/android/os/Process.java b/core/java/android/os/Process.java
index 93860aa..5118f1a 100644
--- a/core/java/android/os/Process.java
+++ b/core/java/android/os/Process.java
@@ -654,7 +654,7 @@
      * distinct apps running under it each with their own uid.
      */
     public static final int myUserHandle() {
-        return UserId.getUserId(myUid());
+        return UserHandle.getUserId(myUid());
     }
 
     /**
@@ -662,7 +662,7 @@
      * @hide
      */
     public static final boolean isIsolated() {
-        int uid = UserId.getAppId(myUid());
+        int uid = UserHandle.getAppId(myUid());
         return uid >= FIRST_ISOLATED_UID && uid <= LAST_ISOLATED_UID;
     }