Add script for building en.json

Add dependency on babel-cli and the intl plugins for extracting strings from source.

Include script for combining extracted strings into a single source chrome-i18n file as a binary from this package.

scripts/build-i18n-src.js

@@ -0,0 +1,45 @@
+#!/usr/bin/env node
+
+const fs = require('fs');
+const glob = require('glob');
+const path = require('path');
+const mkdirp = require('mkdirp');
+
+var args = process.argv.slice(2);
+
+if (!args.length) {
+    process.stdout.write('You must specify the messages dir generated by babel-plugin-react-intl.\n');
+    process.exit(1);
+}
+
+const MESSAGES_PATTERN = args.shift() + '/**/*.json';
+
+if (!args.length) {
+    process.stdout.write('A destination directory must be specified.\n');
+    process.exit(1);
+}
+
+const LANG_DIR = args.shift();
+
+// Aggregates the default messages that were extracted from the example app's
+// React components via the React Intl Babel plugin. An error will be thrown if
+// there are messages in different components that use the same `id`. The result
+// is a chromei18n format collection of `id: {message: defaultMessage,
+// description: description}` pairs for the app's default locale.
+let defaultMessages = glob.sync(MESSAGES_PATTERN)
+    .map((filename) => fs.readFileSync(filename, 'utf8'))
+    .map((file) => JSON.parse(file))
+    .reduce((collection, descriptors) => {
+        descriptors.forEach(({id, defaultMessage, description}) => {
+            if (collection.hasOwnProperty(id)) {
+                throw new Error(`Duplicate message id: ${id}`);
+            }
+
+            collection[id] = {message: defaultMessage, description: description};
+        });
+
+        return collection;
+    }, {});
+
+mkdirp.sync(LANG_DIR);
+fs.writeFileSync(path.join(LANG_DIR, 'en.json'), JSON.stringify(defaultMessages, null, 2));