KeyStore: Add getApplicationContext method required for Asus Devices

- Since Google migrated keystore to v2 they removed getApplicationContext which is required by Asus Flip Camera MotorService app.
- This fixes following issue

10-14 08:53:32.136  2491  2491 E AndroidRuntime: FATAL EXCEPTION: main
10-14 08:53:32.136  2491  2491 E AndroidRuntime: Process: com.asus.motorservice, PID: 2491
10-14 08:53:32.136  2491  2491 E AndroidRuntime: java.lang.NoSuchMethodError: No static method getApplicationContext()Landroid/content/Context; in class Landroid/security/KeyStore; or its super classes (declaration of 'android.security.KeyStore' appears in /system/framework/framework.jar!classes2.dex)
10-14 08:53:32.136  2491  2491 E AndroidRuntime:   at com.asus.motorservice.t.<init>(Unknown Source:29)

Change-Id: I9c95000a8f3d26022bad4a5db85eb8de48f8aa49
Signed-off-by: Jackeagle <[email protected]>

keystore/java/android/security/KeyStore.java

@@ -16,7 +16,10 @@
 
 package android.security;
 
+import android.app.ActivityThread;
+import android.app.Application;
 import android.compat.annotation.UnsupportedAppUsage;
+import android.content.Context;
 import android.os.Build;
 import android.os.StrictMode;
 
@@ -37,6 +40,17 @@ public class KeyStore {
 
     private static final KeyStore KEY_STORE = new KeyStore();
 
+    /** @hide */
+    @UnsupportedAppUsage
+    public static Context getApplicationContext() {
+        Application application = ActivityThread.currentApplication();
+        if (application == null) {
+            throw new IllegalStateException(
+                    "Failed to obtain application Context from ActivityThread");
+        }
+        return application;
+    }
+
     @UnsupportedAppUsage
     public static KeyStore getInstance() {
         return KEY_STORE;