public void onStart() {
    Preconditions.checkNotNull(mTag);
    Preconditions.checkNotNull(mPerfListener);
    if (mState == ImageRequestState.STARTED) {
      onCancellation();
    }
    mStartTime = System.currentTimeMillis();
    mFinishTime = 0;
    mPerfListener.reportStart();
    mState = ImageRequestState.STARTED;
    FLog.i(TAG, "Image [%s]: loading started...", mTag);
  }
Tracks state of image request.

<p>Components that implement {@link Instrumented} interface can use this class to track their
requests.
samples/comparison/src/main/java/com/facebook/samples/comparison/instrumentation/Instrumentation.java