VR: Animate opacity of the loading indicator

This gives the fade in/out effect on the loading progress bar that 2D UI
now has.

BUG=853821
R=tiborg

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:linux_vr;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: I3d07e2ea005c0fbaafb9042a257b3eac4979a4e9
Reviewed-on: https://chromium-review.googlesource.com/1104984
Commit-Queue: Christopher Grant <cjgrant@chromium.org>
Reviewed-by: Tibor Goldschwendt <tiborg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568425}

chrome/browser/vr/ui_scene_creator.cc

@@ -1425,6 +1425,7 @@ void UiSceneCreator::CreateContentQuad() {
   indicator_bg->SetTranslate(0, kLoadingIndicatorYOffset, 0);
   indicator_bg->SetCornerRadii(
       {0, 0, kContentCornerRadius, kContentCornerRadius});
+  indicator_bg->SetTransitionedProperties({OPACITY});
   VR_BIND_VISIBILITY(indicator_bg, model->loading);
   VR_BIND_COLOR(model_, indicator_bg.get(),
                 &ColorScheme::loading_indicator_background, &Rect::SetColor);

chrome/browser/vr/ui_unittest.cc

@@ -781,6 +781,7 @@ TEST_F(UiTest, LoadingIndicatorBindings) {
 
   model_->loading = true;
   model_->load_progress = 0;
+  RunForMs(100);
   EXPECT_TRUE(
       VerifyVisibility({kLoadingIndicator, kLoadingIndicatorForeground}, true));
   EXPECT_EQ(foreground->GetClipRect(), gfx::RectF(0, 0, 0, 1));