Show Overlay Scrollbar when GestureScrollUpdate

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 2719 matching lines @@
     host_impl_->active_tree()->BuildPropertyTreesForTesting();
     host_impl_->active_tree()->DidBecomeActive();
     DrawFrame();
   }
 
   void RunTest(LayerTreeSettings::ScrollbarAnimator animator) {
     LayerTreeSettings settings = DefaultSettings();
     settings.scrollbar_animator = animator;
     settings.scrollbar_fade_in_delay = base::TimeDelta::FromMilliseconds(20);
     settings.scrollbar_fade_out_delay = base::TimeDelta::FromMilliseconds(20);
+    settings.scrollbar_fade_out_resize_delay =
+        base::TimeDelta::FromMilliseconds(20);
     settings.scrollbar_fade_out_duration =
         base::TimeDelta::FromMilliseconds(20);
 
     // If no animator is set, scrollbar won't show and no animation is expected.
     bool expecting_animations = animator != LayerTreeSettings::NO_ANIMATOR;
 
     SetupLayers(settings);
 
     base::TimeTicks fake_now = base::TimeTicks::Now();
 
     if (expecting_animations) {
       // A task will be posted to fade the initial scrollbar.
       EXPECT_FALSE(did_request_next_frame_);
       EXPECT_FALSE(did_request_redraw_);
       EXPECT_FALSE(animation_task_.Equals(base::Closure()));
       requested_animation_delay_ = base::TimeDelta();
       animation_task_ = base::Closure();
     } else {
       EXPECT_FALSE(did_request_next_frame_);
       EXPECT_FALSE(did_request_redraw_);
       EXPECT_TRUE(animation_task_.Equals(base::Closure()));
       EXPECT_EQ(base::TimeDelta(), requested_animation_delay_);
     }
 
-    // If no scroll happened during a scroll gesture, it should have no effect.
+    // If no scroll happened during a scroll gesture, it appears scrollbars and

[bokan, 2017/02/27 23:34:17]

I would leave this case as is and make sure no GSU means no effect. Add a test
below that checks that an empty ScrollBy queues an animation. Also, please add a
check for !ScrollbarsHidden

+    // schedules a fade out delay.
     host_impl_->ScrollBegin(BeginState(gfx::Point()).get(),
                             InputHandler::WHEEL);
+    host_impl_->ScrollBy(UpdateState(gfx::Point(), gfx::Vector2dF(0, 0)).get());
     host_impl_->ScrollEnd(EndState().get());
     EXPECT_FALSE(did_request_next_frame_);
     EXPECT_FALSE(did_request_redraw_);
-    EXPECT_EQ(base::TimeDelta(), requested_animation_delay_);
-    EXPECT_TRUE(animation_task_.Equals(base::Closure()));
+    if (expecting_animations) {
+      EXPECT_EQ(base::TimeDelta::FromMilliseconds(20),
+                requested_animation_delay_);
+      EXPECT_FALSE(animation_task_.Equals(base::Closure()));
+      requested_animation_delay_ = base::TimeDelta();
+      animation_task_ = base::Closure();
+    } else {
+      EXPECT_EQ(base::TimeDelta(), requested_animation_delay_);
+      EXPECT_TRUE(animation_task_.Equals(base::Closure()));
+    }
 
     // Before the scrollbar animation exists, we should not get redraws.
     BeginFrameArgs begin_frame_args =
         CreateBeginFrameArgsForTesting(BEGINFRAME_FROM_HERE, 0, 2, fake_now);
     host_impl_->WillBeginImplFrame(begin_frame_args);
     host_impl_->Animate();
     EXPECT_FALSE(did_request_next_frame_);
     did_request_next_frame_ = false;
     EXPECT_FALSE(did_request_redraw_);
     did_request_redraw_ = false;
@@ skipping 101 matching lines @@
     host_impl_->ScrollBy(UpdateState(gfx::Point(), gfx::Vector2dF(5, 0)).get());
     EXPECT_FALSE(did_request_next_frame_);
     EXPECT_TRUE(did_request_redraw_);
     did_request_redraw_ = false;
     EXPECT_EQ(base::TimeDelta(), requested_animation_delay_);
     EXPECT_TRUE(animation_task_.Equals(base::Closure()));
 
     host_impl_->ScrollEnd(EndState().get());
     EXPECT_FALSE(did_request_next_frame_);
     EXPECT_FALSE(did_request_redraw_);
-    EXPECT_EQ(base::TimeDelta(), requested_animation_delay_);
-    EXPECT_TRUE(animation_task_.Equals(base::Closure()));
+
+    if (expecting_animations) {
+      EXPECT_EQ(base::TimeDelta::FromMilliseconds(20),

[bokan, 2017/02/27 23:34:16]

Is this because the layer is already scrolled to the maximum offset so
previously it wouldn't have queued an animation?

[chaopeng, 2017/02/28 01:51:12]

Yes,
https://cs.chromium.org/chromium/src/cc/trees/layer_tree_host_impl_unittest.c...

+                requested_animation_delay_);
+      EXPECT_FALSE(animation_task_.Equals(base::Closure()));
+      requested_animation_delay_ = base::TimeDelta();
+      animation_task_ = base::Closure();
+    } else {
+      EXPECT_EQ(base::TimeDelta(), requested_animation_delay_);
+      EXPECT_TRUE(animation_task_.Equals(base::Closure()));
+    }
 
     // Changing page scale triggers scrollbar animation.
     host_impl_->active_tree()->PushPageScaleFromMainThread(1.f, 1.f, 4.f);
     host_impl_->active_tree()->SetPageScaleOnActiveTree(1.1f);
     EXPECT_FALSE(did_request_next_frame_);
     EXPECT_FALSE(did_request_redraw_);
     if (expecting_animations) {
       EXPECT_EQ(base::TimeDelta::FromMilliseconds(20),
                 requested_animation_delay_);
       EXPECT_FALSE(animation_task_.Equals(base::Closure()));
@@ skipping 8953 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