overview: Revise misleading comment

There is a comment that speaks of handling "when there is a window being
dragged" but only checks if the active window is being dragged. It seems
based on a mistaken assumption that a dragged window must be active. The
behavior is actually reasonable because the purpose is to avoid stealing
activation from a dragged window, which is not a concern if the dragged
window is already inactive. Only the comment needs to be fixed.

Bug: None
Change-Id: I390eccc6370ad4ed7d15f2d32212fe43b0233633
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2031641Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737858}

ash/wm/overview/overview_controller.cc

@@ -396,9 +396,7 @@ void OverviewController::ToggleOverview(
         break;
       }
     }
-    // |should_focus_overview_| should also be false if overview starts when
-    // there is a window being dragged. Do not change the window activation as
-    // it might cause the unnecessary shelf item activition indicator change.
+    // Avoid stealing activation from a dragged active window.
     if (should_focus_overview_) {
       aura::Window* active_window = window_util::GetActiveWindow();
       if (active_window && WindowState::Get(active_window)->is_dragged()) {