Add FadeOut delay animation to MouseLeave

cc/input/scrollbar_animation_controller_thinning_unittest.cc

 // Copyright 2013 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/input/scrollbar_animation_controller_thinning.h"
 
 #include "cc/layers/solid_color_scrollbar_layer_impl.h"
 #include "cc/test/fake_impl_task_runner_provider.h"
 #include "cc/test/fake_layer_tree_host_impl.h"
 #include "cc/test/geometry_test_utils.h"
@@ skipping 928 matching lines @@
   EXPECT_FLOAT_EQ(kIdleThicknessScale,
                   v_scrollbar_layer_->thumb_thickness_scale_factor());
   EXPECT_FLOAT_EQ(kIdleThicknessScale,
                   h_scrollbar_layer_->thumb_thickness_scale_factor());
 
   // An animation should have been enqueued.
   EXPECT_FALSE(client_.start_fade().is_null());
   EXPECT_EQ(kDelayBeforeStarting, client_.delay());
 }
 
+// Ensure we have a delay fadeout animation after mouse leave.

[bokan, 2017/02/10 15:50:58]

The key is there's a mouse leave without a mouse move. I'd add "after mouse
leave without a mouse move" to the comment.

+TEST_F(ScrollbarAnimationControllerThinningTest, MouseLeaveFadeOut) {
+  base::TimeTicks time;
+  time += base::TimeDelta::FromSeconds(1);
+
+  // Move mouse near scrollbar.
+  scrollbar_controller_->DidMouseMoveNear(VERTICAL, 1);
+
+  // Scroll to make the scrollbars visible.
+  scrollbar_controller_->DidScrollBegin();
+  scrollbar_controller_->DidScrollUpdate(false);
+  scrollbar_controller_->DidScrollEnd();
+
+  // Should not have delay fadeout animation.
+  EXPECT_TRUE(client_.start_fade().is_null() ||
+              client_.start_fade().IsCancelled());
+
+  // Mouse leave.
+  scrollbar_controller_->DidMouseLeave();
+
+  // An animation should have been enqueued.
+  EXPECT_FALSE(client_.start_fade().is_null());
+  EXPECT_EQ(kDelayBeforeStarting, client_.delay());
+}
+
 }  // namespace
 }  // namespace cc