Disable scrollbar snapback on desktop Linux (Reland)

content/renderer/webscrollbarbehavior_impl_gtkoraura.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 "content/renderer/webscrollbarbehavior_impl_gtkoraura.h"
-
-#include "build/build_config.h"
-#include "third_party/WebKit/public/platform/WebPoint.h"
-#include "third_party/WebKit/public/platform/WebRect.h"
-
-namespace content {
-
-bool WebScrollbarBehaviorImpl::shouldCenterOnThumb(
-      blink::WebPointerProperties::Button mouseButton,
-      bool shiftKeyPressed,
-      bool altKeyPressed) {
-#if (defined(OS_LINUX) && !defined(OS_CHROMEOS))
-  if (mouseButton == blink::WebPointerProperties::Button::Middle)
-    return true;
-#endif
-  return (mouseButton == blink::WebPointerProperties::Button::Left) &&
-      shiftKeyPressed;
-}
-
-bool WebScrollbarBehaviorImpl::shouldSnapBackToDragOrigin(
-    const blink::WebPoint& eventPoint,
-    const blink::WebRect& scrollbarRect,
-    bool isHorizontal) {
-  // Constants used to figure the drag rect outside which we should snap the
-  // scrollbar thumb back to its origin. These calculations are based on
-  // observing the behavior of the MSVC8 main window scrollbar + some
-  // guessing/extrapolation.
-  static const int kOffEndMultiplier = 3;
-  static const int kOffSideMultiplier = 8;
-  static const int kDefaultWinScrollbarThickness = 17;
-
-  // Find the rect within which we shouldn't snap, by expanding the track rect
-  // in both dimensions.
-  gfx::Rect noSnapRect(scrollbarRect);
-  int thickness = isHorizontal ? noSnapRect.height() : noSnapRect.width();
-  // Even if the platform's scrollbar is narrower than the default Windows one,
-  // we still want to provide at least as much slop area, since a slightly
-  // narrower scrollbar doesn't necessarily imply that users will drag
-  // straighter.
-  thickness = std::max(thickness, kDefaultWinScrollbarThickness);
-  noSnapRect.Inset(
-      (isHorizontal ? kOffEndMultiplier : kOffSideMultiplier) * -thickness,
-      (isHorizontal ? kOffSideMultiplier : kOffEndMultiplier) * -thickness);
-
-  // On most platforms, we should snap iff the event is outside our calculated
-  // rect.  On Linux, however, we should not snap for events off the ends, but
-  // not the sides, of the rect.
-#if (defined(OS_LINUX) && !defined(OS_CHROMEOS))
-  return isHorizontal ?
-      (eventPoint.y < noSnapRect.y() || eventPoint.y >= noSnapRect.bottom()) :
-      (eventPoint.x < noSnapRect.x() || eventPoint.x >= noSnapRect.right());
-#else
-  return !noSnapRect.Contains(eventPoint);
-#endif
-}
-
-}  // namespace content