Update usage of ActivityManagerNative.

- Remove references to ActivityManagerProxy.
- Add isSystemReady to ActivityManager.

Bug: 30977067
Test: cts/hostsidetests/services/activityandwindowmanager/util/run-test android.server.cts
      adb shell am instrument -e class com.android.server.am.ActivityManagerTest,com.android.server.am.TaskStackChangedListenerTest \
          -w com.android.frameworks.servicestests/android.support.test.runner.AndroidJUnitRunner
Change-Id: I07390b6124fb1515821f5c0b37baf6ae74adc8fa
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/phone/PhoneStatusBarPolicy.java b/packages/SystemUI/src/com/android/systemui/statusbar/phone/PhoneStatusBarPolicy.java
index 032c86b..9ee1e8f 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/phone/PhoneStatusBarPolicy.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/phone/PhoneStatusBarPolicy.java
@@ -17,7 +17,6 @@
 package com.android.systemui.statusbar.phone;
 
 import android.app.ActivityManager;
-import android.app.ActivityManagerNative;
 import android.app.AlarmManager;
 import android.app.AlarmManager.AlarmClockInfo;
 import android.app.SynchronousUserSwitchObserver;
@@ -146,7 +145,7 @@
 
         // listen for user / profile change.
         try {
-            ActivityManagerNative.getDefault().registerUserSwitchObserver(mUserSwitchListener, TAG);
+            ActivityManager.getService().registerUserSwitchObserver(mUserSwitchListener, TAG);
         } catch (RemoteException e) {
             // Ignore
         }
@@ -380,7 +379,7 @@
         UserInfo user = null;
         if (userId == UserHandle.USER_CURRENT) {
             try {
-                user = ActivityManagerNative.getDefault().getCurrentUser();
+                user = ActivityManager.getService().getCurrentUser();
             } catch (RemoteException e) {
                 // Ignore
             }