Show Overlay Scrollbar when GestureScrollUpdate

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 148 matching lines @@
   return animated;
 }
 
 float ScrollbarAnimationController::AnimationProgressAtTime(
     base::TimeTicks now) {
   base::TimeDelta delta = now - last_awaken_time_;
   float progress = delta.InSecondsF() / fade_out_duration_.InSecondsF();
   return std::max(std::min(progress, 1.f), 0.f);
 }
 
-void ScrollbarAnimationController::DidScrollBegin() {
-  currently_scrolling_ = true;
-}
-
 void ScrollbarAnimationController::RunAnimationFrame(float progress) {
   ApplyOpacityToScrollbars(1.f - progress);
   client_->SetNeedsRedrawForScrollbarAnimation();
   if (progress == 1.f)
     StopAnimation();
 }
 
-void ScrollbarAnimationController::DidScrollUpdate(bool on_resize) {
+void ScrollbarAnimationController::DidScrollBegin() {
+  currently_scrolling_ = true;
+}
+
+void ScrollbarAnimationController::DidScrollEnd() {
+  bool has_scrolled = scroll_gesture_has_scrolled_;
+  scroll_gesture_has_scrolled_ = false;
+
+  currently_scrolling_ = false;
+
+  // We don't fade out scrollbar if they need thinning animation and mouse is
+  // near.
+  if (need_thinning_animation_ && MouseIsNearAnyScrollbar())
+    return;
+
+  if (has_scrolled)
+    PostDelayedFadeOut(false);
+}
+
+void ScrollbarAnimationController::DidScrollUpdate() {
   if (need_thinning_animation_ && Captured())
     return;
 
   StopAnimation();
 
   // As an optimization, we avoid spamming fade delay tasks during active fast
   // scrolls.  But if we're not within one, we need to post every scroll update.
   if (!currently_scrolling_) {
     // We don't fade out scrollbar if they need thinning animation and mouse is
     // near.
     if (!need_thinning_animation_ || !MouseIsNearAnyScrollbar())
-      PostDelayedFadeOut(on_resize);
+      PostDelayedFadeOut(false);
   } else {
     scroll_gesture_has_scrolled_ = true;
   }
 
   Show();
 
   if (need_thinning_animation_) {
     vertical_controller_->UpdateThumbThicknessScale();
     horizontal_controller_->UpdateThumbThicknessScale();
   }
 }
 
-void ScrollbarAnimationController::DidScrollEnd() {
-  bool has_scrolled = scroll_gesture_has_scrolled_;
-  scroll_gesture_has_scrolled_ = false;
+void ScrollbarAnimationController::WillUpdateScroll() {
+  if (need_thinning_animation_)

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

Instead of using need_thinning_animation_, add a bool
show_scrollbars_on_scroll_gesture_ and set it appropriately in the constructors.

+    DidScrollUpdate();
+}
 
-  currently_scrolling_ = false;
-
-  // We don't fade out scrollbar if they need thinning animation and mouse is
-  // near.
-  if (need_thinning_animation_ && MouseIsNearAnyScrollbar())
-    return;
-
-  if (has_scrolled)
-    PostDelayedFadeOut(false);
+void ScrollbarAnimationController::DidResize() {
+  StopAnimation();
+  Show();
+  // We should use the gesture delay rather than the resize delay if we're in a
+  // gesture scroll, even if it is resizing.
+  PostDelayedFadeOut(!currently_scrolling_);
 }
 
 void ScrollbarAnimationController::DidMouseDown() {
   if (!need_thinning_animation_ || ScrollbarsHidden())
     return;
 
   vertical_controller_->DidMouseDown();
   horizontal_controller_->DidMouseDown();
 }
 
@@ skipping 134 matching lines @@
   bool previouslyVisible = opacity_ > 0.0f;
   bool currentlyVisible = opacity > 0.0f;
 
   opacity_ = opacity;
 
   if (previouslyVisible != currentlyVisible)
     client_->DidChangeScrollbarVisibility();
 }
 
 }  // namespace cc