overview: Avoid bailing out of UpdateDragIndicatorsAndOverviewGrid

OverviewWindowDragController::UpdateDragIndicatorsAndOverviewGrid()
contains code that bails out if the window cannot be snapped in split
view. So then OverviewSession::RearrangeDuringDrag() does not get
called, and it has responsibility for updating the drop target
background visibility, hence Issue 964469. Also,
OverviewSession::SetSplitViewDragIndicatorsIndicatorState() does not get
called, and it has responsibility for reparenting the split view drag
indicators widget so that it appears on the correct display, meaning
that the present CL is a step toward fixing Issue 961171, although the
present CL certainly does not completely fix Issue 961171.

Test: manual
Bug: 961171, 964469
Change-Id: I95704caacfb315161c9ecf34e3ad55b1c40a8c2c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1617272Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661078}

ash/wm/overview/overview_window_drag_controller.cc

@@ -309,27 +309,23 @@ void OverviewWindowDragController::UpdateDragIndicatorsAndOverviewGrid(
   if (!ShouldUpdateDragIndicatorsOrSnap(location_in_screen))
     return;
 
-  // Attempt to update the drag indicators and move the window grid only if the
-  // window is snappable.
-  if (!CanSnapInSplitview(item_->GetWindow())) {
-    snap_position_ = SplitViewController::NONE;
-    return;
-  }
-
-  snap_position_ = GetSnapPosition(location_in_screen);
   IndicatorState indicator_state;
-  switch (snap_position_) {
-    case SplitViewController::NONE:
-      indicator_state = CanSnapInSplitview(item_->GetWindow())
-                            ? IndicatorState::kDragArea
-                            : IndicatorState::kCannotSnap;
-      break;
-    case SplitViewController::LEFT:
-      indicator_state = IndicatorState::kPreviewAreaLeft;
-      break;
-    case SplitViewController::RIGHT:
-      indicator_state = IndicatorState::kPreviewAreaRight;
-      break;
+  if (CanSnapInSplitview(item_->GetWindow())) {
+    snap_position_ = GetSnapPosition(location_in_screen);
+    switch (snap_position_) {
+      case SplitViewController::NONE:
+        indicator_state = IndicatorState::kDragArea;
+        break;
+      case SplitViewController::LEFT:
+        indicator_state = IndicatorState::kPreviewAreaLeft;
+        break;
+      case SplitViewController::RIGHT:
+        indicator_state = IndicatorState::kPreviewAreaRight;
+        break;
+    }
+  } else {
+    snap_position_ = SplitViewController::NONE;
+    indicator_state = IndicatorState::kCannotSnap;
   }
   overview_session_->RearrangeDuringDrag(item_->GetWindow(), location_in_screen,
                                          indicator_state);