getDebugger_(block) {
      let debugDrawer = this.blockToDebugger[block.id];

      if (!debugDrawer) {
        this.regiserWorkspaceListener_(block.workspace);
        debugDrawer = new DebugRenderer.DebugDrawerClass(this.getConstants());
        this.blockToDebugger[block.id] = debugDrawer;
      }
      return debugDrawer;
    }
Gets the debug renderer for the given block.
If we have already created a debugger for this block, use that debugger
so that it can remove any previously created html elements.
@param {Blockly.BlockSvg} block The block that is about to be rendered.
@returns {DebugDrawer} The object used to draw the debug rectangles
    on the block.
@private