Fix setPlay logic for lottie

SetPlay does not work if the animation is not loaded. Update it to set
the autoplay attribite if the animation is not loaded yet.

Bug: None
Test: Manual Test
Change-Id: I8132d11b5fd9ae77002f79cab7f0e12ef4e91c91
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879855Reviewed-by: Malay Keshav <malaykeshav@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Yue Li <updowndota@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709996}

chrome/test/data/webui/cr_elements/cr_lottie_tests.js

@@ -129,6 +129,24 @@ cr.define('cr_lottie_test', function() {
     await waitForPlayingEventAgain;
   });
 
+  test('TestPlayBeforeInit', async () => {
+    assertTrue(crLottieElement.autoplay);
+
+    crLottieElement.setPlay(false);
+    assertFalse(crLottieElement.autoplay);
+
+    crLottieElement.setPlay(true);
+    assertTrue(crLottieElement.autoplay);
+
+    const waitForInitializeEvent =
+        test_util.eventToPromise('cr-lottie-initialized', crLottieElement);
+    await waitForInitializeEvent;
+
+    const waitForPlayingEvent =
+        test_util.eventToPromise('cr-lottie-playing', crLottieElement);
+    await waitForPlayingEvent;
+  });
+
   test('TestRenderFrame', async () => {
     // Offscreen canvas has a race issue when used in this test framework. To
     // ensure that we capture a frame from the animation and not an empty frame,

ui/webui/resources/cr_elements/chromeos/cr_lottie/cr_lottie.js

@@ -80,6 +80,8 @@ Polymer({
   setPlay: function(shouldPlay) {
     if (this.isAnimationLoaded_) {
       this.worker_.postMessage({control: {play: shouldPlay}});
+    } else {
+      this.autoplay = shouldPlay;
     }
   },