Function startProfiling

packages/react-devtools-shared/src/backend/fiber/renderer.js:7624–7666

(
    shouldRecordChangeDescriptions: boolean,
    shouldRecordTimeline: boolean,
  )

  }

  function startProfiling(
    shouldRecordChangeDescriptions: boolean,
    shouldRecordTimeline: boolean,
  ) {
    if (isProfiling) {
      return;
    }

    recordChangeDescriptions = shouldRecordChangeDescriptions;
    recordTimeline = shouldRecordTimeline;

    // Capture initial values as of the time profiling starts.
    // It's important we snapshot both the durations and the id-to-root map,
    // since either of these may change during the profiling session
    // (e.g. when a fiber is re-rendered or when a fiber gets removed).
    displayNamesByRootID = new Map();
    initialTreeBaseDurationsMap = new Map();

    hook.getFiberRoots(rendererID).forEach(root => {
      const rootInstance = rootToFiberInstanceMap.get(root);
      if (rootInstance === undefined) {
        throw new Error(
          'Expected the root instance to already exist when starting profiling',
        );
      }
      const rootID = rootInstance.id;
      ((displayNamesByRootID: any): DisplayNamesByRootID).set(
        rootID,
        getDisplayNameForRoot(root.current),
      );
      const initialTreeBaseDurations: Array<[number, number]> = [];
      snapshotTreeBaseDurations(rootInstance, initialTreeBaseDurations);
      (initialTreeBaseDurationsMap: any).set(rootID, initialTreeBaseDurations);
    });

    isProfiling = true;
    profilingStartTime = getCurrentTime();
    rootToCommitProfilingMetadataMap = new Map();

    if (toggleProfilingStatus !== null) {
      toggleProfilingStatus(true, recordTimeline);
    }
  }

  function stopProfiling() {
    isProfiling = false;