shelf: Allow gestures to scroll the overflow shelf.

This gives users a way to reach apps when the overflow is beyond filled
on tablet mode. Also fix a bug with the shelf layout manager handling
events on the overflow.

Test: manual
Bug: 808237
Change-Id: Ia3d4a14c8c1a15f7c991a201bdad94d6657f4e6d
Reviewed-on: https://chromium-review.googlesource.com/1208826Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589221}

ash/shelf/overflow_bubble_view.cc

@@ -84,6 +84,17 @@ void OverflowBubbleView::InitOverflowBubble(views::View* anchor,
   AddChildView(shelf_view_);
 }
 
+void OverflowBubbleView::ProcessGestureEvent(const ui::GestureEvent& event) {
+  if (event.type() != ui::ET_GESTURE_SCROLL_UPDATE)
+    return;
+
+  if (shelf_->IsHorizontalAlignment())
+    ScrollByXOffset(static_cast<int>(-event.details().scroll_x()));
+  else
+    ScrollByYOffset(static_cast<int>(-event.details().scroll_y()));
+  Layout();
+}
+
 void OverflowBubbleView::ScrollByXOffset(int x_offset) {
   const gfx::Rect visible_bounds(GetContentsBounds());
   const gfx::Size contents_size(shelf_view_->GetPreferredSize());
@@ -158,8 +169,10 @@ bool OverflowBubbleView::OnMouseWheel(const ui::MouseWheelEvent& event) {
 }
 
 void OverflowBubbleView::OnScrollEvent(ui::ScrollEvent* event) {
-  ScrollByXOffset(-event->x_offset());
-  ScrollByYOffset(-event->y_offset());
+  if (shelf_->IsHorizontalAlignment())
+    ScrollByXOffset(static_cast<int>(-event->x_offset()));
+  else
+    ScrollByYOffset(static_cast<int>(-event->y_offset()));
   Layout();
   event->SetHandled();
 }

ash/shelf/overflow_bubble_view.h

@@ -27,6 +27,9 @@ class ASH_EXPORT OverflowBubbleView : public views::BubbleDialogDelegateView,
   // ShelfView containing the overflow items.
   void InitOverflowBubble(views::View* anchor, ShelfView* shelf_view);
 
+  // Scrolls the bubble contents if it is a scroll update event.
+  void ProcessGestureEvent(const ui::GestureEvent& event);
+
   // views::BubbleDialogDelegateView:
   int GetDialogButtons() const override;
   gfx::Rect GetBubbleBounds() override;
@@ -40,13 +43,13 @@ class ASH_EXPORT OverflowBubbleView : public views::BubbleDialogDelegateView,
   void ScrollByXOffset(int x_offset);
   void ScrollByYOffset(int y_offset);
 
-  // views::View overrides:
+  // views::View:
   gfx::Size CalculatePreferredSize() const override;
   void Layout() override;
   void ChildPreferredSizeChanged(views::View* child) override;
   bool OnMouseWheel(const ui::MouseWheelEvent& event) override;
 
-  // ui::EventHandler overrides:
+  // ui::EventHandler:
   void OnScrollEvent(ui::ScrollEvent* event) override;
 
   // ShelfBackgroundAnimatorObserver:

ash/shelf/shelf_view.cc

@@ -1790,6 +1790,15 @@ void ShelfView::ViewHierarchyChanged(
 }
 
 void ShelfView::OnGestureEvent(ui::GestureEvent* event) {
+  // Do not forward events to |shelf_| (which forwards events to the shelf
+  // layout manager) as we do not want gestures on the overflow to open the app
+  // list for example.
+  if (is_overflow_mode()) {
+    main_shelf_->overflow_bubble()->bubble_view()->ProcessGestureEvent(*event);
+    event->StopPropagation();
+    return;
+  }
+
   // Convert the event location from current view to screen, since swiping up on
   // the shelf can open the fullscreen app list. Updating the bounds of the app
   // list during dragging is based on screen coordinate space.