MacViews: Fix scrolling when clicking on the views::ScrollView scroll track

ui/views/controls/scrollbar/cocoa_scroll_bar.mm

 // Copyright 2016 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.
 
 #import "ui/views/controls/scrollbar/cocoa_scroll_bar.h"
 
 #import "base/mac/sdk_forward_declarations.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "third_party/skia/include/effects/SkGradientShader.h"
 #include "ui/compositor/layer.h"
@@ skipping 272 matching lines @@
 bool CocoaScrollBar::OnMousePressed(const ui::MouseEvent& event) {
   // Ignore the mouse press if the scrollbar is hidden.
   if (IsScrollbarFullyHidden())
     return false;
 
   return BaseScrollBar::OnMousePressed(event);
 }
 
 void CocoaScrollBar::OnMouseReleased(const ui::MouseEvent& event) {
   ResetOverlayScrollbar();
+  BaseScrollBar::OnMouseReleased(event);
 }
 
 void CocoaScrollBar::OnMouseEntered(const ui::MouseEvent& event) {
   if (scroller_style_ != NSScrollerStyleOverlay)
     return;
 
   // If the scrollbar thumb did not completely fade away, then reshow it when
   // the mouse enters the scrollbar thumb.
   if (!IsScrollbarFullyHidden())
     ShowScrollbar();
@@ skipping 175 matching lines @@
 void CocoaScrollBar::SetScrolltrackVisible(bool visible) {
   has_scrolltrack_ = visible;
   SchedulePaint();
 }
 
 CocoaScrollBarThumb* CocoaScrollBar::GetCocoaScrollBarThumb() const {
   return static_cast<CocoaScrollBarThumb*>(GetThumb());
 }
 
 }  // namespace views