overview: Fix GetGridBoundsInScreenForSplitview

The present CL modifies GetGridBoundsInScreenForSplitview so that it
uses the correct split view controller when on an external display.

SplitViewOverviewSessionInClamshellTestMultiDisplayOnly.Dragging

Test: ash_unittests
Bug: 1019221
Change-Id: Ibba4867a342d6a4057e7bb724fbd24b0dae85d77
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1887837
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710575}

ash/wm/overview/overview_session_unittest.cc

@@ -5445,8 +5445,10 @@ TEST_P(SplitViewOverviewSessionInClamshellTestMultiDisplayOnly, Dragging) {
   std::unique_ptr<aura::Window> window1 = CreateTestWindow(bounds_within_root2);
   std::unique_ptr<aura::Window> window2 = CreateTestWindow(bounds_within_root2);
   ToggleOverview();
-  OverviewItem* item1 = GetOverviewItemForWindow(window1.get());
-  OverviewItem* item2 = GetOverviewItemForWindow(window2.get());
+  OverviewGrid* grid_on_root2 =
+      overview_session()->GetGridWithRootWindow(root_windows[1]);
+  OverviewItem* item1 = grid_on_root2->GetOverviewItemContaining(window1.get());
+  OverviewItem* item2 = grid_on_root2->GetOverviewItemContaining(window2.get());
   SplitViewController* split_view_controller =
       SplitViewController::Get(root_windows[1]);
   SplitViewDragIndicators* indicators =
@@ -5460,6 +5462,9 @@ TEST_P(SplitViewOverviewSessionInClamshellTestMultiDisplayOnly, Dragging) {
   overview_session()->Drag(item1, right_snap_point);
   EXPECT_EQ(IndicatorState::kPreviewAreaRight,
             indicators->current_indicator_state());
+  EXPECT_EQ(SplitViewController::Get(root_windows[1])
+                ->GetSnappedWindowBoundsInScreen(SplitViewController::LEFT),
+            grid_on_root2->bounds());
   overview_session()->CompleteDrag(item1, right_snap_point);
   EXPECT_EQ(SplitViewController::State::kRightSnapped,
             split_view_controller->state());

ash/wm/overview/overview_utils.cc

@@ -224,8 +224,7 @@ void MaximizeIfSnapped(aura::Window* window) {
 gfx::Rect GetGridBoundsInScreenForSplitview(
     aura::Window* window,
     base::Optional<IndicatorState> indicator_state) {
-  auto* split_view_controller =
-      SplitViewController::Get(Shell::GetPrimaryRootWindow());
+  auto* split_view_controller = SplitViewController::Get(window);
   auto state = split_view_controller->state();
 
   // If we are in splitview mode already just use the given state, otherwise