Greylist com.google.vr.platform hidden methods

Enforcement of non-SDK API is being extended to all modules on the
boot class path. This includes the com.google.vr.platform package,
which is used to set up VR on a given device. Two hidden methods
are used by the client static library via reflection. Mark them
@UnsupportedAppUsage so that they remain discoverable.

Bug: 111911841
Test: make
Change-Id: I2ac9d91ad24194c3205adad1d333649bfd3d2bec

vr/java/com/google/vr/platform/DeviceInfo.java

@@ -1,5 +1,6 @@
 package com.google.vr.platform;
 
+import android.annotation.UnsupportedAppUsage;
 import android.os.SystemProperties;
 
 /**
@@ -13,6 +14,7 @@ public class DeviceInfo {
     /**
      * Returns true if this device boots directly in VR mode.
      */
+    @UnsupportedAppUsage
     public static boolean getVrBoot() {
         return SystemProperties.getBoolean(VR_MODE_BOOT, false);
     }

vr/java/com/google/vr/platform/Dvr.java

@@ -1,5 +1,7 @@
 package com.google.vr.platform;
 
+import android.annotation.UnsupportedAppUsage;
+
 /**
  * Class to load the dvr api.
  * @hide
@@ -10,6 +12,7 @@ public class Dvr {
      *
      * @return A Long object describing the handle returned by dlopen.
      */
+    @UnsupportedAppUsage
     public static Long loadLibrary() {
         // Load a thin JNI library that runs dlopen on request.
         System.loadLibrary("dvr_loader");