Don't fade in overlay scrollbar when user interacting the content under scrollbar.

cc/input/scrollbar_animation_controller.cc

 // Copyright 2014 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.h"
 
 #include <algorithm>
 
 #include "base/time/time.h"
 #include "cc/trees/layer_tree_impl.h"
@@ skipping 84 matching lines @@
   DCHECK(need_thinning_animation_);
   if (orientation == ScrollbarOrientation::VERTICAL)
     return *(vertical_controller_.get());
   else
     return *(horizontal_controller_.get());
 }
 
 void ScrollbarAnimationController::StartAnimation() {
   DCHECK(animation_change_ != NONE);
   delayed_scrollbar_animation_.Cancel();
+  need_trigger_scrollbar_fade_in_ = false;
   is_animating_ = true;
   last_awaken_time_ = base::TimeTicks();
   client_->SetNeedsAnimateForScrollbarAnimation();
 }
 
 void ScrollbarAnimationController::StopAnimation() {
   delayed_scrollbar_animation_.Cancel();
+  need_trigger_scrollbar_fade_in_ = false;
   is_animating_ = false;
   animation_change_ = NONE;
 }
 
 void ScrollbarAnimationController::PostDelayedAnimation(
     AnimationChange animation_change) {
   animation_change_ = animation_change;
   delayed_scrollbar_animation_.Cancel();
   delayed_scrollbar_animation_.Reset(
       base::Bind(&ScrollbarAnimationController::StartAnimation,
@@ skipping 95 matching lines @@
 void ScrollbarAnimationController::WillUpdateScroll() {
   if (show_scrollbars_on_scroll_gesture_)
     DidScrollUpdate();
 }
 
 void ScrollbarAnimationController::DidRequestShowFromMainThread() {
   DidScrollUpdate();
 }
 
 void ScrollbarAnimationController::DidMouseDown() {
-  if (!need_thinning_animation_ || ScrollbarsHidden())
+  if (!need_thinning_animation_)
     return;
 
+  if (ScrollbarsHidden()) {
+    if (need_trigger_scrollbar_fade_in_) {
+      delayed_scrollbar_animation_.Cancel();
+      need_trigger_scrollbar_fade_in_ = false;
+    }
+    return;
+  }
+
   vertical_controller_->DidMouseDown();
   horizontal_controller_->DidMouseDown();
 }
 
 void ScrollbarAnimationController::DidMouseUp() {
-  if (!need_thinning_animation_ || !Captured())
+  if (!need_thinning_animation_)
     return;
 
+  if (!Captured()) {
+    if (MouseIsNearAnyScrollbar() && ScrollbarsHidden()) {
+      PostDelayedAnimation(FADE_IN);
+      need_trigger_scrollbar_fade_in_ = true;
+    }
+    return;
+  }
+
   vertical_controller_->DidMouseUp();
   horizontal_controller_->DidMouseUp();
 
-  if (!MouseIsNearAnyScrollbar())
+  if (!MouseIsNearAnyScrollbar() && !ScrollbarsHidden()) {

[bokan, 2017/06/08 14:02:38]

Nit: no braces

     PostDelayedAnimation(FADE_OUT);
+  }
 }
 
 void ScrollbarAnimationController::DidMouseLeave() {
   if (!need_thinning_animation_)
     return;
 
   vertical_controller_->DidMouseLeave();
   horizontal_controller_->DidMouseLeave();
 
   delayed_scrollbar_animation_.Cancel();
   need_trigger_scrollbar_fade_in_ = false;
 
   if (ScrollbarsHidden() || Captured())
     return;
 
   PostDelayedAnimation(FADE_OUT);
 }
 
 void ScrollbarAnimationController::DidMouseMove(
-    const gfx::PointF& device_viewport_point) {
+    const gfx::PointF& device_viewport_point,
+    bool is_mouse_down) {
   if (!need_thinning_animation_)
     return;
 
   bool need_trigger_scrollbar_fade_in_before = need_trigger_scrollbar_fade_in_;
 
   vertical_controller_->DidMouseMove(device_viewport_point);
   horizontal_controller_->DidMouseMove(device_viewport_point);
 
-  need_trigger_scrollbar_fade_in_ = MouseIsNearAnyScrollbar();
-
   if (Captured())

[bokan, 2017/06/08 14:02:38]

Could you add a DCHECK that if we're Captured() the scrollbars must not be
hidden.

     return;
 
   if (ScrollbarsHidden()) {
+    // Do not fade in scrollbar when user interacting with the content below
+    // scrollbar.
+    if (is_mouse_down)
+      return;
+    need_trigger_scrollbar_fade_in_ = MouseIsNearAnyScrollbar();
     if (need_trigger_scrollbar_fade_in_before !=
         need_trigger_scrollbar_fade_in_) {
       if (need_trigger_scrollbar_fade_in_) {
         PostDelayedAnimation(FADE_IN);
       } else {
         delayed_scrollbar_animation_.Cancel();
       }
     }
   } else {
     if (MouseIsNearAnyScrollbar()) {
@@ skipping 60 matching lines @@
   if (opacity_ != opacity)
     client_->SetNeedsRedrawForScrollbarAnimation();
 
   opacity_ = opacity;
 
   if (previouslyVisible != currentlyVisible)
     client_->DidChangeScrollbarVisibility();
 }
 
 }  // namespace cc