feat(GoogleMapsMixin): create mixin for context usage

src/GoogleMapsMixin.js

@@ -0,0 +1,52 @@
+/** @jsx React.DOM */
+"use strict";
+var React = require("react/addons");
+
+module.exports = {
+
+  getInitialState () {
+    return {
+      googleMapsApi: this.props.googleMapsApi,
+      map: null
+    };
+  },
+
+  childContextTypes: {
+    getMap: React.PropTypes.func,
+    getApi: React.PropTypes.func,
+    hasMap: React.PropTypes.func,
+    _set_map: React.PropTypes.func
+  },
+
+  contextTypes: {
+    getMap: React.PropTypes.func,
+    getApi: React.PropTypes.func,
+    hasMap: React.PropTypes.func,
+    _set_map: React.PropTypes.func
+  },
+
+  getChildContext () {
+    return {
+      getMap: this._get_map,
+      getApi: this._get_api,
+      hasMap: this._has_map,
+      _set_map: this._set_map
+    };
+  },
+
+  _get_map () {
+    return this.state.map;
+  },
+
+  _get_api () {
+    return this.state.googleMapsApi;
+  },
+
+  _has_map () {
+    return !!this._get_map();
+  },
+
+  _set_map (map) {
+    this.setState({ map });
+  }
+};