code: public function onLayoutGenerate(Varien_Event_Observer $observer)
      {
          if (!$this->canCollect()) {
              return;
          }
  
          /** @var Mage_Core_Model_Layout $layout */
          $layout = $observer->getData('layout');
          $requestInfo = $this->getRequestInfo();
  
          // Adds block description for all blocks generated by layout
          $layoutBlocks = $layout->getAllBlocks();
          foreach ($layoutBlocks as $block) {
              if (!$this->canCaptureBlock($block)) {
                  continue;
              }
  
              $requestInfo->addBlock($block);
          }
  
          // Update design information
          /** @var Mage_Core_Model_Design_Package $design */
          $design = Mage::getSingleton('core/design_package');
          $requestInfo->addLayout($layout, $design);
  
          // Save profiler information to get a generated token before rendering toolbar
          $this->saveProfiling();
      }
docs: Listens to controller_action_layout_generate_blocks_after and records
  instantiated blocks
  
  @param Varien_Event_Observer $observer