@Override
  public void trim(MemoryTrimType trimType) {
    if (!mSemaphore.tryAcquire()) {
      return;
    }
    try {
      mByteArraySoftRef.clear();
    } finally {
      mSemaphore.release();
    }
  }
Responds to memory pressure by simply 'discarding' the local byte array if it is not used at
the moment.

@param trimType kind of trimming to perform (ignored)
imagepipeline/src/main/java/com/facebook/imagepipeline/memory/SharedByteArray.java