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/wm/InputMonitor.java b/services/core/java/com/android/server/wm/InputMonitor.java
index a8eb75c..12c72e9 100644
--- a/services/core/java/com/android/server/wm/InputMonitor.java
+++ b/services/core/java/com/android/server/wm/InputMonitor.java
@@ -26,7 +26,7 @@
 import static com.android.server.wm.WindowManagerDebugConfig.DEBUG_TASK_POSITIONING;
 import static com.android.server.wm.WindowManagerDebugConfig.TAG_WM;
 
-import android.app.ActivityManagerNative;
+import android.app.ActivityManager;
 import android.graphics.Rect;
 import android.os.Debug;
 import android.os.Looper;
@@ -252,7 +252,7 @@
             try {
                 // Notify the activity manager about the timeout and let it decide whether
                 // to abort dispatching or keep waiting.
-                long timeout = ActivityManagerNative.getDefault().inputDispatchingTimedOut(
+                long timeout = ActivityManager.getService().inputDispatchingTimedOut(
                         windowState.mSession.mPid, aboveSystem, reason);
                 if (timeout >= 0) {
                     // The activity manager declined to abort dispatching.