Add jni::IsFennec() that returns whether we're in a Fennec environment (defined as the presence of the GeckoApp class). Then, add jni::IsFennec() checks to places where we use JNI for Fennec-only classes.
Add jni::IsFennec() that returns whether we're in a Fennec environment (defined as the presence of the GeckoApp class). Then, add jni::IsFennec() checks to places where we use JNI for Fennec-only classes.