NewMessageListView: Respect the swipe direction.

In Notification Center, a notification slides out of the screen when
it's removed. When a notification is removed by touch gesture, it's
natural to respect the direction the user swiped.

See the #6 of the bug for detail.

TEST=manual
BUG=882522

Change-Id: I89389a9e9c0297db855227eece2fe42369d2f96e
Reviewed-on: https://chromium-review.googlesource.com/c/1353057Reviewed-by: Manu Cornet <manucornet@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612056}

ash/system/message_center/unified_message_list_view.cc

@@ -110,6 +110,13 @@ class UnifiedMessageListView::MessageViewContainer
     return message_view_->GetMode() == MessageView::Mode::PINNED;
   }
 
+  // Returns the direction that the notification is swiped out. If swiped to the
+  // left, it returns -1 and if sipwed to the right, it returns 1. By default
+  // (i.e. the notification is removed but not by touch gesture), it returns 1.
+  int GetSlideDirection() const {
+    return message_view_->GetSlideAmount() < 0 ? -1 : 1;
+  }
+
   // views::View:
   void ChildPreferredSizeChanged(views::View* child) override {
     PreferredSizeChanged();
@@ -397,10 +404,11 @@ void UnifiedMessageListView::UpdateBounds() {
   for (int i = 0; i < child_count(); ++i) {
     auto* view = GetContainer(i);
     const int height = view->GetHeightForWidth(kTrayMenuWidth);
+    const int direction = view->GetSlideDirection();
     view->set_start_bounds(view->ideal_bounds());
     view->set_ideal_bounds(
         view->is_removed()
-            ? gfx::Rect(kTrayMenuWidth, y, kTrayMenuWidth, height)
+            ? gfx::Rect(kTrayMenuWidth * direction, y, kTrayMenuWidth, height)
             : gfx::Rect(0, y, kTrayMenuWidth, height));
     y += height;
   }