Add proof of concept test

src/renderers/shared/__tests__/ReactDebugFiberPerf-test.js

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+/**
+ * Copyright 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @emails react-core
+ */
+
+'use strict';
+
+var ReactDOMFeatureFlags = require('ReactDOMFeatureFlags');
+
+describe('ReactDebugFiberPerf', () => {
+  var React;
+  var ReactDOM;
+
+  var currentPeriod = {
+    name: null,
+    label: null,
+    parent: null,
+    children: [],
+  };
+
+  function getFlameChart() {
+    return JSON.stringify(currentPeriod.children[0], null, 2);
+  }
+
+  beforeEach(() => {
+    global.performance = {
+      mark(markName) {
+        var period = {
+          name: markName,
+          label: null,
+          parent: currentPeriod,
+          children: [],
+          toJSON() {
+            return [this.label, ...this.children.map(c => c.toJSON())];
+          }
+        };
+        currentPeriod.children.push(period);
+        currentPeriod = period;
+      },
+      measure(label, markName) {
+        if (markName !== currentPeriod.name) {
+          throw new Error('Unexpected measure() call.');
+        }
+        currentPeriod.label = label;
+        currentPeriod = currentPeriod.parent;
+      },
+      clearMarks() {},
+      clearMeasures() {},
+    };
+    React = require('react');
+    ReactDOM = require('react-dom');
+  });
+
+  function Row() {
+    return <div />;
+  }
+
+  it('runs', () => {
+    if (!ReactDOMFeatureFlags.useFiber) {
+      return;
+    }
+    const container = document.createElement('div');
+    ReactDOM.render(<Row />, container);
+    expect(getFlameChart()).toMatchSnapshot();
+  });
+});

src/renderers/shared/__tests__/__snapshots__/ReactDebugFiberPerf-test.js.snap

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+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`ReactDebugFiberPerf runs 1`] = `
+"[
+  \\"⚛ (React Tree Reconciliation)\\",
+  [
+    \\"⚛ Row [mount]\\"
+  ],
+  [
+    \\"⚛ (Committing Changes)\\",
+    [
+      \\"⚛ (Committing Host Effects: 1 Total)\\"
+    ],
+    [
+      \\"⚛ (Calling Lifecycle Methods: 1 Total)\\"
+    ]
+  ]
+]"
+`;