Revert Perf tool back to core/index.js

src/core/index.js

@@ -6,6 +6,10 @@ import ApisPreset from "core/presets/apis"
 import * as AllPlugins from "core/plugins/all"
 import { parseSearch } from "core/utils"
 
+if (process.env.NODE_ENV !== "production") {
+  window.Perf = require("react-addons-perf")
+}
+
 // eslint-disable-next-line no-undef
 const { GIT_DIRTY, GIT_COMMIT, PACKAGE_VERSION, HOSTNAME, BUILD_TIME } = buildInfo