code: public boolean isInBitmapMemoryCache(final ImageRequest imageRequest) {
      if (imageRequest == null) {
        return false;
      }
      final CacheKey cacheKey = mCacheKeyFactory.getBitmapCacheKey(imageRequest, null);
      CloseableReference<CloseableImage> ref = mBitmapMemoryCache.get(cacheKey);
      try {
        return CloseableReference.isValid(ref);
      } finally {
        CloseableReference.closeSafely(ref);
      }
    }
docs: Returns whether the image is stored in the bitmap memory cache.
  
  @param imageRequest the imageRequest for the image to be looked up.
  @return true if the image was found in the bitmap memory cache, false otherwise.