tablet: Fix bug with screenshot persisting when transitiong while overview.

More details in the bug. The problem was that we would start observing,
but not stop observing. The normal workflow was to stop observing when
the window itself was done animating, but it didn't because it was already
maximized. It would also stop observing, if there was no animation
detected normally, but it didn't because the overview restore animation
was going on.

Move the overview within the scoped observer so that TabletModeController
observes the scheduled animation properly, and will cleanup properly.

Test: manual
Bug: 1002735
Change-Id: I3aff9cc81375a9258db6de57571241ab5bb1f0e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1797110Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695698}

ash/wm/tablet_mode/tablet_mode_window_manager.cc

@@ -233,27 +233,6 @@ aura::Window* TabletModeWindowManager::GetTopWindow() {
 }
 
 void TabletModeWindowManager::Init() {
-  // If clamshell split view mode is not enabled, still keep the old behavior:
-  // end overview if it's active. And carry over snapped windows to splitscreen
-  // if possible.
-  if (!IsClamshellSplitViewModeEnabled())
-    Shell::Get()->overview_controller()->EndOverview();
-
-  // If clamshell splitview mode is enabled, there are 3 cases when entering
-  // tablet mode:
-  // 1) overview is active but split view is inactive: keep overview active in
-  //    tablet mode.
-  // 2) overview and splitview are both active (splitview can only be active
-  //    when overview is active in clamshell mode): keep overview and splitview
-  //    both active in tablet mode.
-  // 3) overview is inactive: keep the current behavior, i.e.,
-  //    a. if the top window is a snapped window, put it in splitview
-  //    b. if the second top window is also a snapped window and snapped to
-  //       the other side, put it in split view as well. Otherwise, open
-  //       overview on the other side of the screen
-  //    c. if the top window is not a snapped window, maximize all windows
-  //       when entering tablet mode.
-
   {
     ScopedObserveWindowAnimation scoped_observe(GetTopWindow(), this,
                                                 /*exiting_tablet_mode=*/false);
@@ -570,6 +549,27 @@ WindowStateType TabletModeWindowManager::GetDesktopWindowStateType(
 }
 
 void TabletModeWindowManager::ArrangeWindowsForTabletMode() {
+  // If clamshell split view mode is not enabled, still keep the old behavior:
+  // end overview if it's active. And carry over snapped windows to
+  // splitscreen if possible.
+  if (!IsClamshellSplitViewModeEnabled())
+    Shell::Get()->overview_controller()->EndOverview();
+
+  // If clamshell splitview mode is enabled, there are 3 cases when entering
+  // tablet mode:
+  // 1) overview is active but split view is inactive: keep overview active in
+  //    tablet mode.
+  // 2) overview and splitview are both active (splitview can only be active
+  //    when overview is active in clamshell mode): keep overview and splitview
+  //    both active in tablet mode.
+  // 3) overview is inactive: keep the current behavior, i.e.,
+  //    a. if the top window is a snapped window, put it in splitview
+  //    b. if the second top window is also a snapped window and snapped to
+  //       the other side, put it in split view as well. Otherwise, open
+  //       overview on the other side of the screen
+  //    c. if the top window is not a snapped window, maximize all windows
+  //       when entering tablet mode.
+
   // |activatable_windows| includes all windows to be tracked, and that includes
   // windows on the lock screen via |scoped_skip_user_session_blocked_check|.
   ScopedSkipUserSessionBlockedCheck scoped_skip_user_session_blocked_check;