Experimental app list slide animation is now horizontal, not vertical.

This makes the lack of proper clipping of WebContents more noticeable,
but it's behind a flag so fixing it isn't urgent.

Note that the animation always slides pages to/from the left side
(previously the top). In the future, the pages will be positioned in the
correct order.

BUG=376068

Review URL: https://codereview.chromium.org/305433002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@272945 0039d316-1c4b-4281-b951-d872f2087c98

ui/app_list/views/apps_grid_view.cc

@@ -358,6 +358,9 @@ AppsGridView::AppsGridView(AppsGridViewDelegate* delegate,
       activated_folder_item_view_(NULL),
       dragging_for_reparent_item_(false) {
   SetPaintToLayer(true);
+  // Clip any icons that are outside the grid view's bounds. These icons would
+  // otherwise be visible to the user when the grid view is off screen.
+  layer()->SetMasksToBounds(true);
   SetFillsBoundsOpaquely(false);
 
   pagination_model_->AddObserver(this);

ui/app_list/views/contents_view.cc

@@ -156,7 +156,7 @@ void ContentsView::CalculateIdealBounds() {
 
     gfx::Rect incoming_target(rect);
     gfx::Rect outgoing_target(rect);
-    outgoing_target.set_y(-outgoing_target.height());
+    outgoing_target.set_x(-outgoing_target.width());
 
     for (int i = 0; i < view_model_->view_size(); ++i) {
       view_model_->set_ideal_bounds(i,