beginWrite_() {
    this.writeInProgress = true;
    this.inProgress.push({
      workspaceId: this.workspaceId,
      entryNumber: this.counter,
      events: Blockly.Events.filter(this.notSent, true),
    });
    this.counter += 1;
    this.notSent = [];
  }
Change status of WorkspaceClient in preparation for the network call.
Set writeInProgress to true, adds a LocalEntry to inProgress based on
the events that were notSent, and clears the notSent array.
@private