Add useVrFlinger() method to SurfaceFlinger ConfigStore

Add useVrFlinger() method to SurfaceFlinger ConfigStore, which is
used to ensure we only start vr flinger on Daydream ready devices.

Bug: 35885165

Test: Checked for "SurfaceFlinger UseVrFlinger" in the logs,
confirmed it only shows up for Daydream ready devices.

Change-Id: I3c39b1f094e28f06b510171fc0968cf71f5d5550
diff --git a/configstore/1.0/default/SurfaceFlingerConfigs.cpp b/configstore/1.0/default/SurfaceFlingerConfigs.cpp
index e8872e8..fc66c59 100644
--- a/configstore/1.0/default/SurfaceFlingerConfigs.cpp
+++ b/configstore/1.0/default/SurfaceFlingerConfigs.cpp
@@ -111,6 +111,18 @@
   return Void();
 }
 
+Return<void> SurfaceFlingerConfigs::useVrFlinger(useVrFlinger_cb _hidl_cb) {
+    bool value = false;
+    bool specified = false;
+#ifdef USE_VR_FLINGER
+    value = true;
+    specified = true;
+#endif
+    _hidl_cb({specified, value});
+    LOG(INFO) << "SurfaceFlinger UseVrFlinger: " << (value ? "true" : "false");
+    return Void();
+}
+
 // Methods from ::android::hidl::base::V1_0::IBase follow.
 ISurfaceFlingerConfigs* HIDL_FETCH_ISurfaceFlingerConfigs(const char* /* name */) {
     return new SurfaceFlingerConfigs();