[Merge to M110] Tooltip: Set parent_window_ null on hiding tooltip

This CL resets `parent_window_` in TooltipLacros on Hide().
This aims to fix the crash on GetHost.
Without this CL, `parent_window_` stays non-null when the window is
destructed, so we sets it null on Hide() which is called when the window
is destroyed via TooltipController::OnWindowDestroyed().

(cherry picked from commit 6af0784)

Bug: 1404163
Change-Id: I14c2a0d238b3d88f35d03664e6ac11a8ee28b7b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4150449
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Eriko Kurimoto <elkurin@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1091022}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4159631
Auto-Submit: Eriko Kurimoto <elkurin@chromium.org>
Cr-Commit-Position: refs/branch-heads/5481@{#257}
Cr-Branched-From: 130f3e4-refs/heads/main@{#1084008}

ui/views/corewm/tooltip_lacros.cc

@@ -118,6 +118,8 @@ void TooltipLacros::Hide() {
   if (platform_window) {
     platform_window->HideTooltip();
   }
+
+  parent_window_ = nullptr;
 }
 
 bool TooltipLacros::IsVisible() {

ui/wm/public/tooltip_observer.h

@@ -24,15 +24,18 @@ class WM_PUBLIC_EXPORT TooltipObserver : public base::CheckedObserver {
  public:
   ~TooltipObserver() override = default;
 
-  // Called when tooltip whose parent window's toplevel window is `target` is
-  // shown. `bounds` is relative to `target` position.
+  // Called when tooltip is shown.
+  // `target` is a target window of show tooltip. This may be null if the target
+  // window is already destroyed,
+  // `bounds` is relative to the target window position.
   // TODO(crbug.com/1385219): Use tooltip's parent window for `target`.
   virtual void OnTooltipShown(aura::Window* target,
                               const std::u16string& text,
                               const gfx::Rect& bounds) = 0;
 
-  // Called when tooltip whose parent window's toplevel window is `target` is
-  // hidden.
+  // Called when tooltip is hidden.
+  // `target` is a target window of show tooltip. This may be null if the target
+  // window is already destroyed,
   // TODO(crbug.com/1385219): Use tooltip's parent window for `target`.
   virtual void OnTooltipHidden(aura::Window* target) = 0;
 };