ctive". To summarize, in order to find First
   * Interactive we look for a long enough window between |searchBegin| and
   * |searchEnd| such that it doesn't contain a heavy task cluster. The required
   * length of the window decreases the further we move away from |searchBegin|.
   * A "task cluster" is defined as a group of long tasks such that they are at
   * least 1s away from any other long task that is not in the group. A task
   * cluster is considered "heavy" if the duration of the task cluster (