fix: issue with gutter width initialization (jquense#1181)

Reproduce the original issue (in Chrome):

1. Directly go to http://intljusticemission.github.io/react-big-calendar/examples/index.html#selectable
2. Notice that you cannot see the day headers because the width of the gutter is set way too big

By wrapping it in the requestAnimationFrame it ensures that it is set after the initial paint is finished (which does the css etc).

src/TimeGrid.js

@@ -99,6 +99,10 @@ export default class TimeGrid extends Component {
     window.removeEventListener('resize', this.handleResize)
 
     raf.cancel(this.rafHandle)
+
+    if (this.measureGutterAnimationFrameRequest) {
+      window.cancelAnimationFrame(this.measureGutterAnimationFrameRequest)
+    }
   }
 
   componentDidUpdate() {
@@ -145,7 +149,7 @@ export default class TimeGrid extends Component {
     let { min, max, components, accessors, localizer } = this.props
 
     const resources = this.memoizedResources(this.props.resources, accessors)
-    const groupedEvents = resources.groupEvents(events) 
+    const groupedEvents = resources.groupEvents(events)
 
     return resources.map(([id, resource], i) =>
       range.map((date, jj) => {
@@ -277,11 +281,18 @@ export default class TimeGrid extends Component {
   }
 
   measureGutter() {
-    const width = getWidth(this.gutter)
-
-    if (width && this.state.gutterWidth !== width) {
-      this.setState({ gutterWidth: width })
+    if (this.measureGutterAnimationFrameRequest) {
+      window.cancelAnimationFrame(this.measureGutterAnimationFrameRequest)
     }
+    this.measureGutterAnimationFrameRequest = window.requestAnimationFrame(
+      () => {
+        const width = getWidth(this.gutter)
+
+        if (width && this.state.gutterWidth !== width) {
+          this.setState({ gutterWidth: width })
+        }
+      }
+    )
   }
 
   applyScroll() {