overscroll: Disable overscroll by default.

content/browser/web_contents/web_contents_view_aura.cc

 // Copyright (c) 2012 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/browser/web_contents/web_contents_view_aura.h"
 
 #include "base/auto_reset.h"
 #include "base/utf_string_conversions.h"
 #include "content/browser/renderer_host/dip_util.h"
 #include "content/browser/renderer_host/overscroll_controller.h"
@@ skipping 710 matching lines @@
 
   return ShouldNavigateForward(web_contents_->GetController(),
                                current_overscroll_gesture_) ?
       overscroll_window_.get() : GetContentNativeView();
 }
 
 gfx::Vector2d WebContentsViewAura::GetTranslationForOverscroll(int delta_x,
                                                                int delta_y) {
   if (current_overscroll_gesture_ == OVERSCROLL_NORTH ||
       current_overscroll_gesture_ == OVERSCROLL_SOUTH) {
-    // Ignore vertical overscroll.
-    return gfx::Vector2d();
+    // For vertical overscroll, always do a resisted drag.
+    const float threshold = GetOverscrollConfig(
+        OVERSCROLL_CONFIG_VERT_RESIST_AFTER);
+    int scroll = GetResistedScrollAmount(abs(delta_y),
+                                         static_cast<int>(threshold));
+    return gfx::Vector2d(0, delta_y < 0 ? -scroll : scroll);
   }
 
   // For horizontal overscroll, scroll freely if a navigation is possible. Do a
   // resistive scroll otherwise.
   const NavigationControllerImpl& controller = web_contents_->GetController();
   const gfx::Rect& bounds = GetViewBounds();
   if (ShouldNavigateForward(controller, current_overscroll_gesture_))
     return gfx::Vector2d(std::max(-bounds.width(), delta_x), 0);
   else if (ShouldNavigateBack(controller, current_overscroll_gesture_))
     return gfx::Vector2d(std::min(bounds.width(), delta_x), 0);
@@ skipping 91 matching lines @@
         RenderWidgetHostViewAura*>(view));
   }
 
   view->Show();
 
   // We listen to drag drop events in the newly created view's window.
   aura::client::SetDragDropDelegate(view->GetNativeView(), this);
 
   RenderWidgetHostImpl* host_impl =
       RenderWidgetHostImpl::From(render_widget_host);
-  if (host_impl->overscroll_controller() &&
-      (!web_contents_->GetDelegate() ||
-       web_contents_->GetDelegate()->CanOverscrollContent())) {
+  if (host_impl->overscroll_controller() && web_contents_->GetDelegate() &&
+      web_contents_->GetDelegate()->CanOverscrollContent()) {
     host_impl->overscroll_controller()->set_delegate(this);
     if (!navigation_overlay_.get())
       navigation_overlay_.reset(new OverscrollNavigationOverlay());
   }
 
   return view;
 }
 
 RenderWidgetHostView* WebContentsViewAura::CreateViewForPopupWidget(
     RenderWidgetHost* render_widget_host) {
@@ skipping 428 matching lines @@
       event.location(),
       gfx::Screen::GetScreenFor(GetNativeView())->GetCursorScreenPoint(),
       ConvertAuraEventFlagsToWebInputEventModifiers(event.flags()));
   if (drag_dest_delegate_)
     drag_dest_delegate_->OnDrop();
   current_drop_data_.reset();
   return current_drag_op_;
 }
 
 }  // namespace content