overscroll: Disable overscroll by default.

content/browser/web_contents/web_contents_view_aura.cc

Index: content/browser/web_contents/web_contents_view_aura.cc
diff --git a/content/browser/web_contents/web_contents_view_aura.cc b/content/browser/web_contents/web_contents_view_aura.cc
index b416ceb1421c9adbae5d857f9f5d500540b25e53..235005970d7876a1338c1c517b2a09169b4613f5 100644
--- a/content/browser/web_contents/web_contents_view_aura.cc
+++ b/content/browser/web_contents/web_contents_view_aura.cc
@@ -728,8 +728,12 @@ 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
@@ -841,9 +845,8 @@ RenderWidgetHostView* WebContentsViewAura::CreateViewForWidget(
 
   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());