Fix overlay scrollbar's response to gesture events.

ui/views/controls/scrollbar/overlay_scroll_bar.cc

Index: ui/views/controls/scrollbar/overlay_scroll_bar.cc
diff --git a/ui/views/controls/scrollbar/overlay_scroll_bar.cc b/ui/views/controls/scrollbar/overlay_scroll_bar.cc
index c7e254a6a026ef8a00f9a3b45c988e7e857faa65..b9f52ef9cd50980d72200be6fad047331c3f8113 100644
--- a/ui/views/controls/scrollbar/overlay_scroll_bar.cc
+++ b/ui/views/controls/scrollbar/overlay_scroll_bar.cc
@@ -62,10 +62,15 @@ gfx::Size OverlayScrollBarThumb::GetPreferredSize() {
 void OverlayScrollBarThumb::OnPaint(gfx::Canvas* canvas) {
   gfx::Rect local_bounds(GetLocalBounds());
   SkPaint paint;
-  int alpha = (GetState() == CustomButton::STATE_HOVERED ||
-               GetState() == CustomButton::STATE_PRESSED) ?
-      kThumbHoverAlpha : kThumbDefaultAlpha;
-  alpha *= animation_opacity_;
+  int alpha = kThumbDefaultAlpha * animation_opacity_;
+  if (GetState() == CustomButton::STATE_HOVERED) {
+    alpha = kThumbHoverAlpha * animation_opacity_;
+  } else if(GetState() == CustomButton::STATE_PRESSED) {
+    // If we are in pressed state, no need to worry about animation,
+    // just display the deeper color.
+    alpha = kThumbHoverAlpha;
+  }
+
   paint.setStyle(SkPaint::kFill_Style);
   paint.setColor(SkColorSetARGB(alpha, 0, 0, 0));
   canvas->DrawRoundRect(local_bounds, kThumbCornerRadius, paint);
@@ -119,6 +124,14 @@ void OverlayScrollBar::OnMouseExitedScrollView(const ui::MouseEvent& event) {
   animation_.Hide();
 }
 
+void OverlayScrollBar::OnGestureEvent(ui::GestureEvent* event) {
+  if (event->type() == ui::ET_GESTURE_SCROLL_BEGIN)
+    animation_.Show();
+  else if (event->type() == ui::ET_GESTURE_SCROLL_END)
+    animation_.Hide();

[Jun Mukai, 2013/06/13 19:11:23]

The scrollbar doesn't hide when I fling the scroll view.  It seems that
ET_SCROLL_FLING_START is triggered in that case.

Unfortunately FLING doesn't have END event, which means you'll probably have to
have a timer for closing. Or that's fine to just close immediately, since the
scrollbar doesn't support velocity-move for fling right now.

Another approach is to catch the ET_TOUCH_PRESSED/ET_TOUCH_RELEASED
OnTouchEvent, this will need to add some handler to ScrollView though.

Either is fine to me.

[Jun Mukai, 2013/06/21 21:12:43]

How did you address the issue I commented?  As far as I checked locally, the
scrollbar still doesn't hide for the fling behavior.

+  BaseScrollBar::OnGestureEvent(event);
+}
+
 gfx::Size OverlayScrollBar::GetPreferredSize() {
   return gfx::Size();
 }