Record scroll_layer_id instead of scrollbar_animation_controller pointer

cc/trees/layer_tree_host_impl_unittest.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <cmath>
@@ skipping 11735 matching lines @@
 
   // Capture scrollbar_1, then move mouse to scrollbar_2's layer, should post an
   // event to fade out scrollbar_1.
   animation_task_ = base::Closure();
 
   host_impl_->MouseDown();
   host_impl_->MouseMoveAt(gfx::Point(100, 150));
   host_impl_->MouseUp();
 
   EXPECT_FALSE(animation_task_.Equals(base::Closure()));
+
+  // Near scrollbar_1, then mouse down and unregister
+  // scrollbar_2_animation_controller, then mouse up should not cause crash.
+  host_impl_->MouseMoveAt(gfx::Point(40, 150));
+  host_impl_->MouseDown();
+  host_impl_->UnregisterScrollbarAnimationController(root_scroll->id());
+  host_impl_->MouseUp();
 }
 
 TEST_F(LayerTreeHostImplTest,
        LayerTreeHostImplTestScrollbarStatesInMainThreadScorlling) {
   SetupMouseMoveAtTestScrollbarStates(true);
 }
 
 TEST_F(LayerTreeHostImplTest,
        LayerTreeHostImplTestScrollbarStatesInNotMainThreadScorlling) {
   SetupMouseMoveAtTestScrollbarStates(false);
@@ skipping 70 matching lines @@
     else
       EXPECT_FALSE(tile->HasRasterTask());
   }
   Region expected_invalidation(
       raster_source->GetRectForImage(checkerable_image->uniqueID()));
   EXPECT_EQ(expected_invalidation, *(root->GetPendingInvalidation()));
 }
 
 }  // namespace
 }  // namespace cc