MessageController: return all messages by sent at, not just 1

ts/test-both/util/iterables_test.ts

@@ -7,6 +7,7 @@ import * as sinon from 'sinon';
 import {
   concat,
   filter,
+  find,
   groupBy,
   isIterable,
   map,
@@ -211,6 +212,29 @@ describe('iterable utilities', () => {
     });
   });
 
+  describe('find', () => {
+    const isOdd = (n: number) => Boolean(n % 2);
+
+    it('returns undefined if the value is not found', () => {
+      assert.isUndefined(find([], isOdd));
+      assert.isUndefined(find([2, 4], isOdd));
+    });
+
+    it('returns the first matching value', () => {
+      assert.strictEqual(find([0, 1, 2, 3], isOdd), 1);
+    });
+
+    it('only iterates until a value is found', () => {
+      function* numbers() {
+        yield 2;
+        yield 3;
+        throw new Error('this should never happen');
+      }
+
+      find(numbers(), isOdd);
+    });
+  });
+
   describe('groupBy', () => {
     it('returns an empty object if passed an empty iterable', () => {
       const fn = sinon.fake();