Enable VR Shell for release build too

base/android/proguard/chromium_code.flags

Index: base/android/proguard/chromium_code.flags
diff --git a/base/android/proguard/chromium_code.flags b/base/android/proguard/chromium_code.flags
index be3186fc9b3316b25c15506b12f8a8d153f7ba10..a2ad4404f73e592038848a033d0028e2ca24ba25 100644
--- a/base/android/proguard/chromium_code.flags
+++ b/base/android/proguard/chromium_code.flags
@@ -34,6 +34,9 @@
 -keepclasseswithmembers class * {
   @org.chromium.base.annotations.UsedByReflection <methods>;
 }
+-keepclasseswithmembers class * {
+  @org.chromium.base.annotations.UsedByReflection <fields>;
+}
 -keepclasseswithmembers,includedescriptorclasses class * {
   native <methods>;
 }