Iframe/div MD scrollbars get idle when mouse leaves the nested elements.

cc/trees/layer_tree_host_impl_unittest.cc

Index: cc/trees/layer_tree_host_impl_unittest.cc
diff --git a/cc/trees/layer_tree_host_impl_unittest.cc b/cc/trees/layer_tree_host_impl_unittest.cc
index de7eb4f281d773882b321171860e5d9cf4446209..b9758420d3ce5e177e82e5de8beecfd7bd65084c 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -3230,15 +3230,13 @@ void LayerTreeHostImplTest::SetupMouseMoveAtWithDeviceScale(
   EXPECT_TRUE(scrollbar_animation_controller->mouse_is_near_scrollbar());
 
   did_request_redraw_ = false;
-  EXPECT_EQ(Layer::INVALID_ID,
-            host_impl_->scroll_layer_id_when_mouse_over_scrollbar());
+  EXPECT_FALSE(scrollbar_animation_controller->mouse_is_over_scrollbar());
   host_impl_->MouseMoveAt(gfx::Point(10, 100));
-  EXPECT_EQ(117, host_impl_->scroll_layer_id_when_mouse_over_scrollbar());
+  EXPECT_TRUE(scrollbar_animation_controller->mouse_is_over_scrollbar());
   host_impl_->MouseMoveAt(gfx::Point(10, 120));
-  EXPECT_EQ(117, host_impl_->scroll_layer_id_when_mouse_over_scrollbar());
+  EXPECT_TRUE(scrollbar_animation_controller->mouse_is_over_scrollbar());
   host_impl_->MouseMoveAt(gfx::Point(150, 120));
-  EXPECT_EQ(Layer::INVALID_ID,
-            host_impl_->scroll_layer_id_when_mouse_over_scrollbar());
+  EXPECT_FALSE(scrollbar_animation_controller->mouse_is_over_scrollbar());
 }
 
 TEST_F(LayerTreeHostImplTest, MouseMoveAtWithDeviceScaleOf1) {