overview: Fix OverviewWindowDragController::GetSnapPosition

OverviewWindowDragController::GetSnapPosition uses the split view
divider position as though it is relative to the whole screen. It is
actually relative to the work area.

Test: ash_unittests SplitViewOverviewSessionInClamshellTestMultiDisplayOnly.Dragging
Bug: 1019219
Change-Id: I8530e53f70f5b5c62c5c4cbedd078abd835ceb16
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1887653Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710452}

ash/wm/overview/overview_session_unittest.cc

@@ -93,6 +93,7 @@
 #include "ui/views/controls/label.h"
 #include "ui/views/widget/widget.h"
 #include "ui/wm/core/coordinate_conversion.h"
+#include "ui/wm/core/cursor_manager.h"
 #include "ui/wm/core/shadow_controller.h"
 #include "ui/wm/core/window_util.h"
 
@@ -5435,6 +5436,56 @@ TEST_P(SplitViewOverviewSessionInClamshellTestMultiDisplayOnly,
   EXPECT_FALSE(InOverviewSession());
 }
 
+// Test dragging to snap an overview item on an external display.
+TEST_P(SplitViewOverviewSessionInClamshellTestMultiDisplayOnly, Dragging) {
+  UpdateDisplay("800x600,800x600");
+  aura::Window::Windows root_windows = Shell::GetAllRootWindows();
+  ASSERT_EQ(2u, root_windows.size());
+  const gfx::Rect bounds_within_root2(800, 0, 400, 400);
+  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());
+  SplitViewController* split_view_controller =
+      SplitViewController::Get(root_windows[1]);
+  SplitViewDragIndicators* indicators =
+      overview_session()->split_view_drag_indicators();
+
+  Shell::Get()->cursor_manager()->SetDisplay(
+      display::Screen::GetScreen()->GetDisplayNearestWindow(root_windows[1]));
+  overview_session()->InitiateDrag(item1, item1->target_bounds().CenterPoint(),
+                                   /*is_touch_dragging=*/false);
+  const gfx::PointF right_snap_point(1599.f, 300.f);
+  overview_session()->Drag(item1, right_snap_point);
+  EXPECT_EQ(IndicatorState::kPreviewAreaRight,
+            indicators->current_indicator_state());
+  overview_session()->CompleteDrag(item1, right_snap_point);
+  EXPECT_EQ(SplitViewController::State::kRightSnapped,
+            split_view_controller->state());
+  EXPECT_EQ(window1.get(), split_view_controller->right_window());
+
+  overview_session()->InitiateDrag(item2, item2->target_bounds().CenterPoint(),
+                                   /*is_touch_dragging=*/false);
+  const gfx::PointF left_of_middle(1150.f, 300.f);
+  overview_session()->Drag(item2, left_of_middle);
+  EXPECT_EQ(IndicatorState::kDragArea, indicators->current_indicator_state());
+  overview_session()->CompleteDrag(item2, left_of_middle);
+  EXPECT_EQ(SplitViewController::State::kRightSnapped,
+            split_view_controller->state());
+  EXPECT_EQ(window1.get(), split_view_controller->right_window());
+
+  overview_session()->InitiateDrag(item2, item2->target_bounds().CenterPoint(),
+                                   /*is_touch_dragging=*/false);
+  const gfx::PointF left_snap_point(810.f, 300.f);
+  overview_session()->Drag(item2, left_snap_point);
+  EXPECT_EQ(IndicatorState::kPreviewAreaLeft,
+            indicators->current_indicator_state());
+  overview_session()->CompleteDrag(item2, left_snap_point);
+  EXPECT_EQ(SplitViewController::State::kNoSnap,
+            split_view_controller->state());
+}
+
 // Verify that when in overview mode, the selector items unsnappable indicator
 // shows up when expected.
 TEST_P(SplitViewOverviewSessionInClamshellTestMultiDisplayOnly,

ash/wm/overview/overview_window_drag_controller.cc

@@ -677,8 +677,9 @@ SplitViewController::SnapPosition OverviewWindowDragController::GetSnapPosition(
   SplitViewController* split_view_controller =
       GetSplitViewControllerForDisplayBeingDraggedIn();
   if (split_view_controller->InSplitViewMode()) {
-    const int position = gfx::ToRoundedInt(
-        is_landscape ? location_in_screen.x() : location_in_screen.y());
+    const int position =
+        gfx::ToRoundedInt(is_landscape ? location_in_screen.x() - area.x()
+                                       : location_in_screen.y() - area.y());
     SplitViewController::SnapPosition default_snap_position =
         split_view_controller->default_snap_position();
     // If we're trying to snap to a position that already has a snapped window: