OverscrollController consumes scroll updates only during gesture-nav.

content/browser/web_contents/aura/gesture_nav_simple.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/browser/web_contents/aura/gesture_nav_simple.h"
 
 #include "cc/layers/layer.h"
 #include "content/browser/frame_host/navigation_controller_impl.h"
 #include "content/browser/renderer_host/overscroll_controller.h"
 #include "content/browser/web_contents/web_contents_impl.h"
@@ skipping 127 matching lines @@
 }
 
 void GestureNavSimple::CompleteGestureAnimation() {
   if (!arrow_)
     return;
   // Make sure the fade-out starts from the complete state.
   ApplyEffectsForDelta(completion_threshold_);
   ApplyEffectsAndDestroy(arrow_->transform(), 0.f);
 }
 
-void GestureNavSimple::ApplyEffectsForDelta(float delta_x) {
+bool GestureNavSimple::ApplyEffectsForDelta(float delta_x) {
   if (!arrow_)
-    return;
+    return false;
   CHECK_GT(completion_threshold_, 0.f);
   CHECK_GE(delta_x, 0.f);
   double complete = std::min(1.f, delta_x / completion_threshold_);
   float translate_x = gfx::Tween::FloatValueBetween(complete, -kArrowWidth, 0);
   gfx::Transform transform;
   transform.Translate(arrow_delegate_->left() ? translate_x : -translate_x,
                       0.f);
   arrow_->SetTransform(transform);
   arrow_->SetOpacity(gfx::Tween::FloatValueBetween(complete, kMinOpacity, 1.f));
+  return true;
 }
 
 gfx::Rect GestureNavSimple::GetVisibleBounds() const {
   return web_contents_->GetNativeView()->bounds();
 }
 
-void GestureNavSimple::OnOverscrollUpdate(float delta_x, float delta_y) {
-  ApplyEffectsForDelta(std::abs(delta_x) + 50.f);
+bool GestureNavSimple::OnOverscrollUpdate(float delta_x, float delta_y) {
+  return ApplyEffectsForDelta(std::abs(delta_x) + 50.f);
 }
 
 void GestureNavSimple::OnOverscrollComplete(OverscrollMode overscroll_mode) {
   CompleteGestureAnimation();
 
   NavigationControllerImpl& controller = web_contents_->GetController();
   if (ShouldNavigateForward(controller, overscroll_mode))
     controller.GoForward();
   else if (ShouldNavigateBack(controller, overscroll_mode))
     controller.GoBack();
@@ skipping 45 matching lines @@
   clip_layer_->SetBounds(window->layer()->bounds());
   clip_layer_->SetMasksToBounds(true);
   clip_layer_->Add(arrow_.get());
 
   ui::Layer* parent = window->layer()->parent();
   parent->Add(clip_layer_.get());
   parent->StackAtTop(clip_layer_.get());
 }
 
 }  // namespace content