public VmTraceData build() {
      for (int i = 0; i < mStackReconstructors.size(); i++) {
        int threadId = mStackReconstructors.keyAt(i);
        CallStackReconstructor reconstructor = mStackReconstructors.valueAt(i);
        mTopLevelCalls.put(threadId, reconstructor.getTopLevel());
      }

      return new VmTraceData(this);
    }