Remove observer in OnConnectionClosed

- Remove observer in OnConnectionClosed instead of Shutdown. Shutdown is
  called in different life cycle. OnConnectionReady can be called more
  than once for a single Shutdown call. It can cause helper bridge to
  register observer more than once.

Bug: 833731
Test: None
Change-Id: I7057f8d11364687f0d7f9fb5d3b5d213a18e18db
Reviewed-on: https://chromium-review.googlesource.com/1018781Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: Yuki Awano <yawano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552236}

chrome/browser/chromeos/arc/accessibility/arc_accessibility_helper_bridge.cc

@@ -193,10 +193,6 @@ void ArcAccessibilityHelperBridge::Shutdown() {
 
   arc_bridge_service_->accessibility_helper()->RemoveObserver(this);
   arc_bridge_service_->accessibility_helper()->SetHost(nullptr);
-
-  auto* surface_manager = ArcNotificationSurfaceManager::Get();
-  if (surface_manager)
-    surface_manager->RemoveObserver(this);
 }
 
 void ArcAccessibilityHelperBridge::OnConnectionReady() {
@@ -216,6 +212,12 @@ void ArcAccessibilityHelperBridge::OnConnectionReady() {
     surface_manager->AddObserver(this);
 }
 
+void ArcAccessibilityHelperBridge::OnConnectionClosed() {
+  auto* surface_manager = ArcNotificationSurfaceManager::Get();
+  if (surface_manager)
+    surface_manager->RemoveObserver(this);
+}
+
 void ArcAccessibilityHelperBridge::OnAccessibilityEventDeprecated(
     mojom::AccessibilityEventType event_type,
     mojom::AccessibilityNodeInfoDataPtr event_source) {

chrome/browser/chromeos/arc/accessibility/arc_accessibility_helper_bridge.h

@@ -63,6 +63,7 @@ class ArcAccessibilityHelperBridge
 
   // ConnectionObserver<mojom::AccessibilityHelperInstance> overrides.
   void OnConnectionReady() override;
+  void OnConnectionClosed() override;
 
   // mojom::AccessibilityHelperHost overrides.
   void OnAccessibilityEventDeprecated(