OverscrollController consumes scroll updates only during gesture-nav.

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/command_line.h"
 #include "base/file_util.h"
 #include "base/metrics/histogram.h"
@@ skipping 1263 matching lines @@
 // WebContentsViewAura, OverscrollControllerDelegate implementation:
 
 gfx::Rect WebContentsViewAura::GetVisibleBounds() const {
   RenderWidgetHostView* rwhv = web_contents_->GetRenderWidgetHostView();
   if (!rwhv || !rwhv->IsShowing())
     return gfx::Rect();
 
   return rwhv->GetViewBounds();
 }
 
-void WebContentsViewAura::OnOverscrollUpdate(float delta_x, float delta_y) {
+bool WebContentsViewAura::OnOverscrollUpdate(float delta_x, float delta_y) {
   if (current_overscroll_gesture_ == OVERSCROLL_NONE)
-    return;
+    return false;
 
   aura::Window* target = GetWindowToAnimateForOverscroll();
   gfx::Vector2d translate = GetTranslationForOverscroll(delta_x, delta_y);
   gfx::Transform transform;
 
   // Vertical overscrolls don't participate in the navigation gesture.
   if (current_overscroll_gesture_ != OVERSCROLL_NORTH &&
       current_overscroll_gesture_ != OVERSCROLL_SOUTH) {
     transform.Translate(translate.x(), translate.y());
     target->SetTransform(transform);
     UpdateOverscrollWindowBrightness(delta_x);
   }
 
   OverscrollUpdateForWebContentsDelegate(translate.y());
+  return translate.x() || translate.y();

[sadrul, 2014/08/18 22:54:09]

return !translate.IsZero();

[tdresser, 2014/08/19 12:51:37]

Done.

 }
 
 void WebContentsViewAura::OnOverscrollComplete(OverscrollMode mode) {
   UMA_HISTOGRAM_ENUMERATION("Overscroll.Completed", mode, OVERSCROLL_COUNT);
   OverscrollUpdateForWebContentsDelegate(0);
   NavigationControllerImpl& controller = web_contents_->GetController();
   if (ShouldNavigateForward(controller, mode) ||
       ShouldNavigateBack(controller, mode)) {
     CompleteOverscrollNavigation(mode);
     return;
@@ skipping 306 matching lines @@
   if (visible) {
     if (!web_contents_->should_normally_be_visible())
       web_contents_->WasShown();
   } else {
     if (web_contents_->should_normally_be_visible())
       web_contents_->WasHidden();
   }
 }
 
 }  // namespace content