overview: Simplify RearrangeDuringDrag and remove unnecessary parameter

The new window dragging state kOtherDisplay added in [1] facilitates
making RearrangeDuringDrag simpler and removing a parameter from it.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1977155

Bug: 961170
Change-Id: Icd4abaaa7f6e7c1d7f055cea76403c7697902500
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1978999
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726879}

ash/wm/overview/overview_grid.cc

@@ -212,6 +212,27 @@ std::unique_ptr<views::Widget> CreateDropTargetWidget(
   return widget;
 }
 
+// Returns 1 if the name of |window_dragging_state| begins with "kFrom," else 0.
+float GetWantedDropTargetOpacity(
+    SplitViewDragIndicators::WindowDraggingState window_dragging_state) {
+  switch (window_dragging_state) {
+    case SplitViewDragIndicators::WindowDraggingState::kNoDrag:
+      return 0.f;
+    case SplitViewDragIndicators::WindowDraggingState::kOtherDisplay:
+      return 0.f;
+    case SplitViewDragIndicators::WindowDraggingState::kFromOverview:
+      return 1.f;
+    case SplitViewDragIndicators::WindowDraggingState::kFromTop:
+      return 1.f;
+    case SplitViewDragIndicators::WindowDraggingState::kFromShelf:
+      return 1.f;
+    case SplitViewDragIndicators::WindowDraggingState::kToSnapLeft:
+      return 0.f;
+    case SplitViewDragIndicators::WindowDraggingState::kToSnapRight:
+      return 0.f;
+  }
+}
+
 // Returns the bounds for the overview window grid according to the split view
 // state. If split view mode is active, the overview window should open on the
 // opposite side of the default snap window. If |divider_changed| is true, maybe
@@ -692,7 +713,6 @@ void OverviewGrid::SetBoundsAndUpdatePositions(
 }
 
 void OverviewGrid::RearrangeDuringDrag(
-    aura::Window* root_window_being_dragged_in,
     aura::Window* dragged_window,
     SplitViewDragIndicators::WindowDraggingState window_dragging_state) {
   OverviewItem* drop_target = GetDropTarget();
@@ -702,12 +722,7 @@ void OverviewGrid::RearrangeDuringDrag(
     ScopedOverviewAnimationSettings settings(
         OVERVIEW_ANIMATION_DROP_TARGET_FADE,
         drop_target_widget_->GetNativeWindow());
-    drop_target->SetOpacity(root_window_being_dragged_in == root_window_ &&
-                                    SplitViewDragIndicators::GetSnapPosition(
-                                        window_dragging_state) ==
-                                        SplitViewController::NONE
-                                ? 1.f
-                                : 0.f);
+    drop_target->SetOpacity(GetWantedDropTargetOpacity(window_dragging_state));
   }
 
   // Update the grid's bounds.
@@ -789,7 +804,7 @@ void OverviewGrid::OnWindowDragContinued(
   DCHECK_EQ(dragged_window_, dragged_window);
   DCHECK_EQ(dragged_window->GetRootWindow(), root_window_);
 
-  RearrangeDuringDrag(root_window_, dragged_window, window_dragging_state);
+  RearrangeDuringDrag(dragged_window, window_dragging_state);
   UpdateDropTargetBackgroundVisibility(nullptr, location_in_screen);
 
   aura::Window* target_window =

ash/wm/overview/overview_grid.h

@@ -146,9 +146,8 @@ class ASH_EXPORT OverviewGrid : public SplitViewObserver,
       bool animate);
 
   // Updates overview bounds and hides the drop target when a preview area is
-  // shown or |root_window_being_dragged_in| does not equal |root_window_|.
+  // shown or the drag is currently outside of |root_window_|.
   void RearrangeDuringDrag(
-      aura::Window* root_window_being_dragged_in,
       aura::Window* dragged_window,
       SplitViewDragIndicators::WindowDraggingState window_dragging_state);
 

ash/wm/overview/overview_session.cc

@@ -358,13 +358,11 @@ void OverviewSession::UpdateSplitViewDragIndicatorsWindowDraggingStates(
   }
 }
 
-void OverviewSession::RearrangeDuringDrag(
-    aura::Window* root_window_being_dragged_in,
-    aura::Window* dragged_window) {
+void OverviewSession::RearrangeDuringDrag(aura::Window* dragged_window) {
   for (std::unique_ptr<OverviewGrid>& grid : grid_list_) {
     DCHECK(grid->split_view_drag_indicators());
     grid->RearrangeDuringDrag(
-        root_window_being_dragged_in, dragged_window,
+        dragged_window,
         grid->split_view_drag_indicators()->current_window_dragging_state());
   }
 }

ash/wm/overview/overview_session.h

@@ -146,8 +146,7 @@ class ASH_EXPORT OverviewSession : public display::DisplayObserver,
       SplitViewController::SnapPosition snap_position);
 
   // See |OverviewGrid::RearrangeDuringDrag|.
-  void RearrangeDuringDrag(aura::Window* root_window_being_dragged_in,
-                           aura::Window* dragged_window);
+  void RearrangeDuringDrag(aura::Window* dragged_window);
 
   // Updates the appearance of each drop target to visually indicate when the
   // dragged window is being dragged over it.

ash/wm/overview/overview_window_drag_controller.cc

@@ -605,12 +605,11 @@ void OverviewWindowDragController::UpdateDragIndicatorsAndOverviewGrid(
     return;
 
   snap_position_ = GetSnapPosition(location_in_screen);
-  aura::Window* root_window = GetRootWindowBeingDraggedIn();
   overview_session_->UpdateSplitViewDragIndicatorsWindowDraggingStates(
-      root_window, /*is_dragging=*/true,
+      GetRootWindowBeingDraggedIn(), /*is_dragging=*/true,
       SplitViewDragIndicators::WindowDraggingState::kFromOverview,
       snap_position_);
-  overview_session_->RearrangeDuringDrag(root_window, item_->GetWindow());
+  overview_session_->RearrangeDuringDrag(item_->GetWindow());
 }
 
 aura::Window* OverviewWindowDragController::GetRootWindowBeingDraggedIn()