Parcel: recycle recycles

Before, it was like getting a used pan with food stuck on it. We run
a clean ship here. You want a Parcel? You get a fresh Parcel. When
we recycle a Parcel, we do a real clean-up job. Air freshener. All
bits brushed over. These Parcel objects are clean as heck now!

(specifically cleans mClassCookies)

Bug: 208279300
Test: build
Change-Id: I250872f5c6796bb64e2dc68008154c0e90feb218

core/java/android/os/Parcel.java

@@ -549,6 +549,7 @@ public final class Parcel {
      */
     public final void recycle() {
         if (DEBUG_RECYCLE) mStack = null;
+        mClassCookies = null;
         freeBuffer();
 
         if (mOwnsNativeParcelObject) {