Masonry experiments warning (pinterest#374)

* wip

* remove canary

.github/pull_request_template.md

@@ -0,0 +1,6 @@
+## TODO
+
+- [ ] Documentation
+- [ ] Tests
+- [ ] Experimental evidence (required for Masonry changes)
+- [ ] Accessibility checkup

dangerfile.js

@@ -3,10 +3,13 @@
 import bundlesize from './scripts/danger/bundlesize.js';
 import changelog from './scripts/danger/changelog.js';
 import lockfile from './scripts/danger/lockfile.js';
+import experiments from './scripts/danger/experiments.js';
 
 // Add a CHANGELOG entry for app changes
 changelog();
 // Keep lockfile up to date with package
 lockfile();
 // Bundle size alerting
 bundlesize();
+// Experimental reminders
+experiments();

scripts/danger/experiments.js

@@ -0,0 +1,13 @@
+// @flow
+
+export default function experiments() {
+  const changed = danger.git.modified_files.some(file =>
+    file.match(/masonry/i)
+  );
+  if (changed) {
+    const title = ':microscope: Experimental data needed';
+    const message =
+      'Changes were made to critical components. Do you have experimental data to back up your changes?';
+    warn(`${title} - <i>${message}</i>`);
+  }
+}