overview: Rewrite bail condition at top of OverviewSession::OnKeyEvent

The present CL rewrites a condition on which OverviewSession::OnKeyEvent
bails out. Instead of checking for clamshell split view mode, it shall
simply check for clamshell mode. This change is a step toward multi-
display support for split view, because it removes a dependency on the
single-display split view functionality.

Test: ash_unittests SplitViewOverviewSessionTest.NoCrashWhenPressTabKey
Bug: 970013
Change-Id: Ibf84a9ab1b41b4481cee3ed6763f92eaeee52f82
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1733713Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683796}

ash/wm/overview/overview_session.cc

@@ -807,9 +807,9 @@ void OverviewSession::OnKeyEvent(ui::KeyEvent* event) {
   // TODO(crbug.com/952315): Explore better ways to handle this splitview +
   // overview + applist case.
   Shell* shell = Shell::Get();
-  if (shell->app_list_controller() &&
-      shell->app_list_controller()->IsVisible() &&
-      Shell::Get()->split_view_controller()->InClamshellSplitViewMode()) {
+  if (!shell->tablet_mode_controller()->InTabletMode() &&
+      shell->app_list_controller() &&
+      shell->app_list_controller()->IsVisible()) {
     return;
   }