overview: Simplify code from CL 1560298

Code from this CL is now unnecessarily complicated (and might have been
so all along):
https://chromium-review.googlesource.com/c/chromium/src/+/1560298
There is no need for OverviewSession::GetGridWithOverviewItem() when we
have OverviewItem::overview_grid(). Then there is also no need for
OverviewSession::AddDropTargetForDraggingFromOverview() or
OverviewSession::RemoveDropTargetForDraggingFromOverview(), as the whole
purpose of putting them in OverviewSession was so that they could call
OverviewSession::GetGridWithOverviewItem(). In fact, currently,
OverviewWindowDragController::CompleteNormalDrag() uses
item_->overview_grid()->RemoveDropTarget() whereas
OverviewWindowDragController::ResetGesture() uses
overview_session_->RemoveDropTargetForDraggingFromOverview(item_), and
there is no reason why they should use different code to remove the drop
target.

Test: manual
Change-Id: Ic973e90d08c9b81b00566306e6b3e3e655939ef4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1628233Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663084}

ash/wm/overview/overview_session.cc

@@ -505,23 +505,12 @@ void OverviewSession::RemoveItem(OverviewItem* overview_item) {
       restore_focus_window_ = nullptr;
   }
 
-  GetGridWithOverviewItem(overview_item)->RemoveItem(overview_item);
+  overview_item->overview_grid()->RemoveItem(overview_item);
   --num_items_;
 
   MaybeCreateAndPositionNoWindowsWidget();
 }
 
-void OverviewSession::AddDropTargetForDraggingFromOverview(
-    OverviewItem* dragged_item) {
-  GetGridWithOverviewItem(dragged_item)
-      ->AddDropTargetForDraggingFromOverview(dragged_item);
-}
-
-void OverviewSession::RemoveDropTargetForDraggingFromOverview(
-    OverviewItem* dragged_item) {
-  GetGridWithOverviewItem(dragged_item)->RemoveDropTarget();
-}
-
 void OverviewSession::InitiateDrag(OverviewItem* item,
                                    const gfx::PointF& location_in_screen) {
   window_drag_controller_ =
@@ -969,11 +958,6 @@ void OverviewSession::OnSplitViewDividerPositionChanged() {
   MaybeCreateAndPositionNoWindowsWidget();
 }
 
-OverviewGrid* OverviewSession::GetGridWithOverviewItem(OverviewItem* item) {
-  DCHECK(GetGridWithRootWindow(item->GetWindow()->GetRootWindow()));
-  return GetGridWithRootWindow(item->GetWindow()->GetRootWindow());
-}
-
 void OverviewSession::ResetFocusRestoreWindow(bool focus) {
   if (!restore_focus_window_)
     return;

ash/wm/overview/overview_session.h

@@ -163,13 +163,6 @@ class ASH_EXPORT OverviewSession : public display::DisplayObserver,
   // repositioned.
   void RemoveItem(OverviewItem* overview_item);
 
-  // Adds a drop target that visually appears to be revealed as |dragged_item|
-  // is dragged off of it.
-  void AddDropTargetForDraggingFromOverview(OverviewItem* dragged_item);
-
-  // Removes the drop target from the grid containing |dragged_item|.
-  void RemoveDropTargetForDraggingFromOverview(OverviewItem* dragged_item);
-
   void InitiateDrag(OverviewItem* item, const gfx::PointF& location_in_screen);
   void Drag(OverviewItem* item, const gfx::PointF& location_in_screen);
   void CompleteDrag(OverviewItem* item, const gfx::PointF& location_in_screen);
@@ -303,9 +296,6 @@ class ASH_EXPORT OverviewSession : public display::DisplayObserver,
  private:
   friend class OverviewSessionTest;
 
-  // Retrieves the window grid containing |item|.
-  OverviewGrid* GetGridWithOverviewItem(OverviewItem* item);
-
   // |focus|, restores focus to the stored window.
   void ResetFocusRestoreWindow(bool focus);
 

ash/wm/overview/overview_window_drag_controller.cc

@@ -192,7 +192,7 @@ void OverviewWindowDragController::StartNormalDragMode(
   original_scaled_size_ = item_->target_bounds().size();
 
   if (should_allow_split_view_) {
-    overview_session_->AddDropTargetForDraggingFromOverview(item_);
+    item_->overview_grid()->AddDropTargetForDraggingFromOverview(item_);
     overview_session_->SetSplitViewDragIndicatorsIndicatorState(
         CanSnapInSplitview(item_->GetWindow()) ? IndicatorState::kDragArea
                                                : IndicatorState::kCannotSnap,
@@ -254,7 +254,7 @@ void OverviewWindowDragController::ResetGesture() {
   if (current_drag_behavior_ == DragBehavior::kNormalDrag) {
     Shell::Get()->mouse_cursor_filter()->HideSharedEdgeIndicator();
     item_->DestroyPhantomsForDragging();
-    overview_session_->RemoveDropTargetForDraggingFromOverview(item_);
+    item_->overview_grid()->RemoveDropTarget();
     overview_session_->SetSplitViewDragIndicatorsIndicatorState(
         IndicatorState::kNone, gfx::Point());
   }