Cros splitscreen: in overview mode, if there is already a snapped win…

…dow, do not allow another window snap to the same position.

Bug: 725683
Change-Id: Ica123477155a7a8d6f3f741c8cc645dfcc0eb812
Reviewed-on: https://chromium-review.googlesource.com/797413
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#527360}

ash/wm/overview/overview_window_drag_controller.cc

@@ -166,9 +166,21 @@ void OverviewWindowDragController::UpdatePhantomWindowAndWindowGrid(
   SplitViewController::SnapPosition last_snap_position = snap_position_;
   snap_position_ = GetSnapPosition(location_in_screen);
 
+  // If there is already a snapped window in |snap_position_|, do not allow
+  // another window snap in the same position.
+  SplitViewController::State snapped_state = split_view_controller_->state();
+  if ((snap_position_ == SplitViewController::LEFT &&
+       snapped_state == SplitViewController::LEFT_SNAPPED) ||
+      (snap_position_ == SplitViewController::RIGHT &&
+       snapped_state == SplitViewController::RIGHT_SNAPPED)) {
+    snap_position_ = SplitViewController::NONE;
+    phantom_window_controller_.reset();
+    return;
+  }
+
   // If there is no current snapped window, update the window grid size if the
   // dragged window can be snapped if dropped.
-  if (split_view_controller_->state() == SplitViewController::NO_SNAP &&
+  if (snapped_state == SplitViewController::NO_SNAP &&
       snap_position_ != last_snap_position) {
     // Do not reposition the item that is currently being dragged.
     window_selector_->SetBoundsForWindowGridsInScreenIgnoringWindow(

ash/wm/overview/window_selector_unittest.cc

@@ -2085,14 +2085,15 @@ TEST_F(SplitViewWindowSelectorTest, DragOverviewWindowToSnap) {
             SplitViewController::LEFT_SNAPPED);
   EXPECT_EQ(split_view_controller()->left_window(), window1.get());
 
-  // Drag |window2| selector item to snap to left.
+  // Drag |window2| selector item to attempt to snap to left. Since there is
+  // already one left snapped window, we do not allow |window2| snap to left.
   WindowSelectorItem* selector_item2 =
       GetWindowItemForWindow(grid_index, window2.get());
   DragWindowTo(selector_item2, gfx::Point(0, 0));
 
   EXPECT_EQ(split_view_controller()->state(),
             SplitViewController::LEFT_SNAPPED);
-  EXPECT_EQ(split_view_controller()->left_window(), window2.get());
+  EXPECT_EQ(split_view_controller()->left_window(), window1.get());
 
   // Drag |window3| selector item to snap to right.
   WindowSelectorItem* selector_item3 =