feat(StreetViewPanorama): update context for children

This allows Marker and OverlayView to be attached to the StreetViewPanorama

src/app/pages/basics/StreetViewPanoramaExample.js

@@ -29,7 +29,7 @@ const StreetViewPanoramaExampleGoogleMap = withGoogleMap(props => (
  * At this point the `GoogleMap` wrapper and `withGoogleMap` HOC become optional, so you can either render map and StreetView
  * at the same time, or just the StreetView on its own
  *    <StreetViewPanorama
- *      element={<div />}
+ *      element={<div style={{ width: `100%`, height: `100%` }} />}
  *      defaultPosition={coordinates}
  *      visible
  *    />

src/lib/StreetViewPanorama.js

@@ -123,6 +123,10 @@ export default _.flowRight(
     [MAP]: PropTypes.object,
   },
 
+  childContextTypes: {
+    [MAP]: PropTypes.object,
+  },
+
   getInitialOptions() {
     return collectUncontrolledAndControlledProps(
       defaultUncontrolledPropTypes,
@@ -131,6 +135,12 @@ export default _.flowRight(
     );
   },
 
+  getChildContext() {
+    return {
+      [MAP]: this.state[STREET_VIEW_PANORAMA],
+    };
+  },
+
   getInitialState() {
     // https://developers.google.com/maps/documentation/javascript/3.exp/reference#StreetViewPanorama
     let streetViewPanorama;
@@ -167,11 +177,13 @@ export default _.flowRight(
   render() {
     if (this.props.element) {
       return (
-        React.cloneElement(this.props.element, {
-          ref: this.handleComponentMount,
-        },
-      ));
+        React.cloneElement(
+          this.props.element,
+          { ref: this.handleComponentMount },
+          this.props.children,
+        )
+      );
     }
-    return false;
+    return <div>{this.props.children}</div>;
   },
 });