Hygiene: enable Babel transpilation

Enable the Babel transpiler so that ES6 template literals,
destructuring, and arrow functions can be used in production.
"last n versions" syntax was not used so that builds are more
reproducible.

Bug: T165036
Change-Id: I553b6d14cc368c7b4366f68d13038c3d505f5429

.babelrc

@@ -0,0 +1,23 @@
+{
+	"presets": [
+		[
+			"env",
+			{
+				// Do not transform modules to CommonJS.
+				"modules": false,
+				// See modern tier: https://www.mediawiki.org/wiki/Compatibility#Browser_support_matrix
+				"targets": {
+					// https://en.wikipedia.org/wiki/Google_Chrome_version_history
+					"chrome": "64",
+					"ie": "11",
+					// https://en.wikipedia.org/wiki/Firefox_version_history
+					"firefox": "58",
+					"safari": "5.1",
+					"opera": "15",
+					"ios": "6.1",
+					"android": "4.1"
+				}
+			}
+		]
+	]
+}

package-lock.json

@@ -546,6 +546,30 @@
         "babel-template": "6.26.0"
       }
     },
+    "babel-loader": {
+      "version": "7.1.4",
+      "resolved": "https://registry.npmjs.org/babel-loader/-/babel-loader-7.1.4.tgz",
+      "integrity": "sha512-/hbyEvPzBJuGpk9o80R0ZyTej6heEOr59GoEUtn8qFKbnx4cJm9FWES6J/iv644sYgrtVw9JJQkjaLW/bqb5gw==",
+      "dev": true,
+      "requires": {
+        "find-cache-dir": "1.0.0",
+        "loader-utils": "1.1.0",
+        "mkdirp": "0.5.1"
+      },
+      "dependencies": {
+        "loader-utils": {
+          "version": "1.1.0",
+          "resolved": "https://registry.npmjs.org/loader-utils/-/loader-utils-1.1.0.tgz",
+          "integrity": "sha1-yYrvSIvM7aL/teLeZG1qdUQp9c0=",
+          "dev": true,
+          "requires": {
+            "big.js": "3.2.0",
+            "emojis-list": "2.1.0",
+            "json5": "0.5.1"
+          }
+        }
+      }
+    },
     "babel-messages": {
       "version": "6.23.0",
       "resolved": "https://registry.npmjs.org/babel-messages/-/babel-messages-6.23.0.tgz",

package.json

@@ -13,6 +13,7 @@
     "precommit": "npm run test:dev && npm run build && git add resources/dist && bundlesize"
   },
   "devDependencies": {
+    "babel-loader": "7.1.4",
     "babel-preset-env": "^1.6.0",
     "babel-register": "^6.24.1",
     "bundlesize": "0.15.3",

webpack.config.js

@@ -48,6 +48,14 @@ conf = {
 	},
 	module: {
 		rules: [
+			{
+				test: /\.js$/,
+				exclude: /node_modules/,
+				use: {
+					loader: 'babel-loader',
+					options: { cacheDirectory: true }
+				}
+			},
 			{
 				test: /\.svg$/,
 				loader: 'svg-inline-loader',