[Merge to M110] Tooltip/Exo: Null check root_surface() before OnToolt…

…ipShown/Hidden

This CL fixes the crash caused by exo::Surface::observers_ being null.
Surface may be set to null by ShellSurfaceBase::OnSurfaceDestroying
while the observer is still alive, so we need to run null check for
OnTooltipShown/Hidden.

(cherry picked from commit 0a32b09)

Bug: 1403331
Change-Id: I1032032070db952a37de5739dac5cfe55cb8cf65
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4123196
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Commit-Queue: Eriko Kurimoto <elkurin@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1086647}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4122378
Cr-Commit-Position: refs/branch-heads/5481@{#217}
Cr-Branched-From: 130f3e4-refs/heads/main@{#1084008}

components/exo/shell_surface_base.cc

@@ -1306,11 +1306,15 @@ void ShellSurfaceBase::OnWindowActivated(ActivationReason reason,
 void ShellSurfaceBase::OnTooltipShown(aura::Window* target,
                                       const std::u16string& text,
                                       const gfx::Rect& bounds) {
-  root_surface()->OnTooltipShown(text, bounds);
+  if (root_surface()) {
+    root_surface()->OnTooltipShown(text, bounds);
+  }
 }
 
 void ShellSurfaceBase::OnTooltipHidden(aura::Window* target) {
-  root_surface()->OnTooltipHidden();
+  if (root_surface()) {
+    root_surface()->OnTooltipHidden();
+  }
 }
 
 // Returns true if surface is currently being resized.