Adjust animation curves of UnifiedSystemTray.

This CL adjusts animation curves of some UnifiedSystemTray elements so
that the animation looks more natural and elements would not overlap
each other.

Detailed spec of the animation curves is still WIP on UX side.

TEST=manual
BUG=858941,857346

Change-Id: Ibdcf9371d5436c5bd7ad6e094dab4b6b88bcf945
Reviewed-on: https://chromium-review.googlesource.com/1124259Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572523}

ash/system/unified/feature_pod_button.cc

@@ -269,7 +269,8 @@ void FeaturePodButton::SetToggled(bool toggled) {
 }
 
 void FeaturePodButton::SetExpandedAmount(double expanded_amount) {
-  label_button_->layer()->SetOpacity(expanded_amount);
+  // TODO(tetsui): Confirm the animation curve with UX.
+  label_button_->layer()->SetOpacity(std::max(0., 5. * expanded_amount - 4.));
   label_button_->SetVisible(expanded_amount > 0.0);
 }
 

ash/system/unified/unified_system_tray_view.cc

@@ -106,15 +106,20 @@ gfx::Size UnifiedSlidersContainerView::CalculatePreferredSize() const {
 }
 
 void UnifiedSlidersContainerView::UpdateOpacity() {
+  const int height = GetPreferredSize().height();
   for (int i = 0; i < child_count(); ++i) {
     views::View* child = child_at(i);
     double opacity = 1.0;
-    if (child->y() > height())
+    if (child->y() > height) {
       opacity = 0.0;
-    else if (child->bounds().bottom() < height())
+    } else if (child->bounds().bottom() < height) {
       opacity = 1.0;
-    else
-      opacity = static_cast<double>(height() - child->y()) / child->height();
+    } else {
+      const double ratio =
+          static_cast<double>(height - child->y()) / child->height();
+      // TODO(tetsui): Confirm the animation curve with UX.
+      opacity = std::max(0., 2. * ratio - 1.);
+    }
     child->layer()->SetOpacity(opacity);
   }
 }