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/services/core/java/com/android/server/BatteryService.java b/services/core/java/com/android/server/BatteryService.java
index b88a45e..573ad63 100644
--- a/services/core/java/com/android/server/BatteryService.java
+++ b/services/core/java/com/android/server/BatteryService.java
@@ -28,7 +28,7 @@
 import com.android.server.lights.Light;
 import com.android.server.lights.LightsManager;
 
-import android.app.ActivityManagerNative;
+import android.app.ActivityManager;
 import android.content.ContentResolver;
 import android.content.Context;
 import android.content.Intent;
@@ -557,7 +557,7 @@
         mHandler.post(new Runnable() {
             @Override
             public void run() {
-                ActivityManagerNative.broadcastStickyIntent(intent, null, UserHandle.USER_ALL);
+                ActivityManager.broadcastStickyIntent(intent, UserHandle.USER_ALL);
             }
         });
     }