Skip cursor client operation in mash.

BUG=833456
TEST=none

Change-Id: I9d01f94670a406ea7b30b4c232775dc76ad4a48c
Reviewed-on: https://chromium-review.googlesource.com/1013272
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: David Reveman <reveman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551282}

components/exo/pointer.cc

@@ -88,7 +88,11 @@ Pointer::Pointer(PointerDelegate* delegate)
   auto* helper = WMHelper::GetInstance();
   helper->AddPreTargetHandler(this);
   helper->AddDisplayConfigurationObserver(this);
-  helper->GetCursorClient()->AddObserver(this);
+  // TODO(sky): CursorClient does not exist in mash
+  // yet. https://crbug.com/631103.
+  aura::client::CursorClient* cursor_client = helper->GetCursorClient();
+  if (cursor_client)
+    cursor_client->AddObserver(this);
 }
 
 Pointer::~Pointer() {
@@ -101,7 +105,11 @@ Pointer::~Pointer() {
   auto* helper = WMHelper::GetInstance();
   helper->RemoveDisplayConfigurationObserver(this);
   helper->RemovePreTargetHandler(this);
-  helper->GetCursorClient()->RemoveObserver(this);
+  // TODO(sky): CursorClient does not exist in mash
+  // yet. https://crbug.com/631103.
+  aura::client::CursorClient* cursor_client = helper->GetCursorClient();
+  if (cursor_client)
+    cursor_client->RemoveObserver(this);
   if (root_surface())
     root_surface()->RemoveSurfaceObserver(this);
 }