Show Overlay Scrollbar when GestureScrollUpdate

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 d271d40b131de04e2908229200b696e8ad110d9c..58206fe0146de71d604d2559ffb89db3326a3979 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -2810,6 +2810,8 @@ class LayerTreeHostImplTestScrollbarAnimation : public LayerTreeHostImplTest {
     settings.scrollbar_animator = animator;
     settings.scrollbar_show_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);
 
@@ -2843,6 +2845,25 @@ class LayerTreeHostImplTestScrollbarAnimation : public LayerTreeHostImplTest {
     EXPECT_EQ(base::TimeDelta(), requested_animation_delay_);
     EXPECT_TRUE(animation_task_.Equals(base::Closure()));
 
+    // For Aura Overlay Scrollbar, if no scroll happened during a scroll
+    // gesture, it appears scrollbars and schedules a delay fade out.

[bokan, 2017/03/09 15:57:58]

nit: "it appears scrollbars and schedules" -> "show scrollbars and schedule"

+    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_);
+    if (animator == LayerTreeSettings::AURA_OVERLAY) {
+      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);
@@ -2950,7 +2971,9 @@ class LayerTreeHostImplTestScrollbarAnimation : public LayerTreeHostImplTest {
       host_impl_->DidFinishImplFrame();
     }
 
-    // Scrollbar animation is not triggered unnecessarily.
+    // For Andrdoid, scrollbar animation is not triggered unnecessarily.
+    // For Aura Overlay Scrollbar, scrollbar appears even scroll offset not

[bokan, 2017/03/09 15:57:58]

nit: "even scroll offset not change" -> "even if scroll offset didn't change"

+    // change.
     host_impl_->ScrollBegin(BeginState(gfx::Point()).get(),
                             InputHandler::WHEEL);
     host_impl_->ScrollBy(UpdateState(gfx::Point(), gfx::Vector2dF(5, 0)).get());
@@ -2963,8 +2986,16 @@ class LayerTreeHostImplTestScrollbarAnimation : public LayerTreeHostImplTest {
     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 (animator == LayerTreeSettings::AURA_OVERLAY) {
+      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()));
+    }
 
     // Changing page scale triggers scrollbar animation.
     host_impl_->active_tree()->PushPageScaleFromMainThread(1.f, 1.f, 4.f);