Make ReactPerf.start() work during reconciliation

src/renderers/shared/ReactDebugTool.js

@@ -79,7 +79,7 @@ function resetMeasurements() {
   var previousMeasurements = currentFlushMeasurements || [];
   var previousOperations = ReactHostOperationHistoryDevtool.getHistory();
 
-  if (!isProfiling || currentFlushNesting === 0) {
+  if (currentFlushNesting === 0) {
     currentFlushStartTime = null;
     currentFlushMeasurements = null;
     clearHistory();
@@ -106,7 +106,7 @@ function checkDebugID(debugID) {
 }
 
 function beginLifeCycleTimer(debugID, timerType) {
-  if (!isProfiling || currentFlushNesting === 0) {
+  if (currentFlushNesting === 0) {
     return;
   }
   warning(
@@ -125,7 +125,7 @@ function beginLifeCycleTimer(debugID, timerType) {
 }
 
 function endLifeCycleTimer(debugID, timerType) {
-  if (!isProfiling || currentFlushNesting === 0) {
+  if (currentFlushNesting === 0) {
     return;
   }
   warning(
@@ -137,11 +137,13 @@ function endLifeCycleTimer(debugID, timerType) {
     currentTimerType || 'no',
     (debugID === currentTimerDebugID) ? 'the same' : 'another'
   );
-  currentFlushMeasurements.push({
-    timerType,
-    instanceID: debugID,
-    duration: performanceNow() - currentTimerStartTime - currentTimerNestedFlushDuration,
-  });
+  if (isProfiling) {
+    currentFlushMeasurements.push({
+      timerType,
+      instanceID: debugID,
+      duration: performanceNow() - currentTimerStartTime - currentTimerNestedFlushDuration,
+    });
+  }
   currentTimerStartTime = null;
   currentTimerNestedFlushDuration = null;
   currentTimerDebugID = null;

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

@@ -467,5 +467,49 @@ describe('ReactPerf', function() {
     expect(console.error.calls.count()).toBe(1);
 
     __DEV__ = true;
-  })
+  });
+
+  it('should work when measurement starts during reconciliation', () => {
+    // https://github.com/facebook/react/issues/6949#issuecomment-230371009
+    var Measurer = React.createClass({
+      componentWillMount() {
+        ReactPerf.start();
+      },
+      componentDidMount() {
+        ReactPerf.stop();
+      },
+      componentWillUpdate() {
+        ReactPerf.start();
+      },
+      componentDidUpdate() {
+        ReactPerf.stop();
+      },
+      render() {
+        // Force reconciliation despite constant element
+        return React.cloneElement(this.props.children);
+      },
+    });
+
+    var container = document.createElement('div');
+    ReactDOM.render(<Measurer><App /></Measurer>, container);
+    expect(ReactPerf.getWasted()).toEqual([]);
+
+    ReactDOM.render(<Measurer><App /></Measurer>, container);
+    expect(ReactPerf.getWasted()).toEqual([{
+      key: 'Measurer',
+      instanceCount: 1,
+      inclusiveRenderDuration: 4,
+      renderCount: 1,
+    }, {
+      key: 'App',
+      instanceCount: 1,
+      inclusiveRenderDuration: 3,
+      renderCount: 1,
+    }, {
+      key: 'App > Box',
+      instanceCount: 2,
+      inclusiveRenderDuration: 2,
+      renderCount: 2,
+    }]);
+  });
 });