Adding momentum/overscroll to views:: ScrollViews

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 8b8ed9cf137fc0230a316305c58a1bbd05a19773..6fdd6b59ed8727686072236e367343f83e30d255 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -289,8 +289,7 @@ LayerTreeHostImpl::~LayerTreeHostImpl() {
     input_handler_client_->WillShutdown();
     input_handler_client_ = NULL;
   }
-  if (scroll_elasticity_helper_)
-    scroll_elasticity_helper_.reset();
+  root_scroll_elasticity_helper_.reset();
 
   // The layer trees must be destroyed before the layer tree host. We've
   // made a contract with our animation controllers that the animation_host
@@ -613,13 +612,33 @@ LayerTreeHostImpl::CreateLatencyInfoSwapPromiseMonitor(
       new LatencyInfoSwapPromiseMonitor(latency, NULL, this));
 }
 
-ScrollElasticityHelper* LayerTreeHostImpl::CreateScrollElasticityHelper() {
-  DCHECK(!scroll_elasticity_helper_);
+ScrollElasticityHelper* LayerTreeHostImpl::CreateRootScrollElasticityHelper() {
+  DCHECK(!root_scroll_elasticity_helper_);
   if (settings_.enable_elastic_overscroll) {
-    scroll_elasticity_helper_.reset(
+    root_scroll_elasticity_helper_.reset(
         ScrollElasticityHelper::CreateForLayerTreeHostImpl(this));
   }
-  return scroll_elasticity_helper_.get();
+  return root_scroll_elasticity_helper_.get();
+}
+
+base::WeakPtr<ScrollElasticityHelper>
+LayerTreeHostImpl::ScrollElasticityHelperForScrollingLayer() {
+  LayerImpl* scrolling_layer_impl = CurrentlyScrollingLayer();
+  if (!scrolling_layer_impl)
+    return nullptr;
+
+  return ScrollElasticityHelperForId(scrolling_layer_impl->id())->GetWeakPtr();
+}
+
+bool LayerTreeHostImpl::ScrollLayerTo(int layer_id,
+                                      const gfx::ScrollOffset& offset) {
+  LayerImpl* layer = active_tree()->FindActiveTreeLayerById(layer_id);
+  if (!layer)
+    return false;
+
+  layer->ScrollBy(
+      ScrollOffsetToVector2dF(offset - layer->CurrentScrollOffset()));
+  return true;
 }
 
 void LayerTreeHostImpl::QueueSwapPromiseForMainThreadScrollUpdate(
@@ -2638,8 +2657,8 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollBeginImpl(
   // in input_handler_proxy instead.
   wheel_scrolling_ = IsWheelBasedScroll(type);
   scroll_state->set_is_direct_manipulation(!wheel_scrolling_);
-  // Invoke |DistributeScrollDelta| even with zero delta and velocity to ensure
-  // scroll customization callbacks are invoked.
+  // Invoke |DistributeScrollDelta| even with zero delta and velocity to process
+  // overscroll and ensure scroll customization callbacks are invoked.
   DistributeScrollDelta(scroll_state);
 
   client_->RenewTreePriority();
@@ -2668,6 +2687,18 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollBegin(
 
   ClearCurrentlyScrollingLayer();
 
+  if (!scroll_state->is_beginning()) {
+    DCHECK(scroll_state->is_in_inertial_phase());
+    // When transitioning into a "flick", try to find the layer that was
+    // already scrolling. Without this, a flick may begin after elastic
+    // overscroll moves the scrolling layer out from beneath the event, causing
+    // a failed hit test.
+    LayerImpl* scrolling_layer_impl =
+        active_tree_->LayerById(active_tree_->LastScrolledLayerId());
+    if (scrolling_layer_impl)
+      return ScrollBeginImpl(scroll_state, scrolling_layer_impl, type);
+  }
+
   gfx::Point viewport_point(scroll_state->position_x(),
                             scroll_state->position_y());
 
@@ -3548,6 +3579,38 @@ LayerTreeHostImpl::ScrollbarAnimationControllerForId(
   return i->second.get();
 }
 
+void LayerTreeHostImpl::RegisterScrollElasticityHelper(int scroll_layer_id) {
+  DCHECK(!InnerViewportScrollLayer() ||
+         scroll_layer_id != InnerViewportScrollLayer()->id());
+  DCHECK(!OuterViewportScrollLayer() ||
+         scroll_layer_id != OuterViewportScrollLayer()->id());
+  DCHECK(settings().enable_elastic_overscroll);
+
+  auto& helper = scroll_elasticity_helpers_[scroll_layer_id];
+  if (!helper)
+    helper = active_tree_->CreateScrollElasticityHelper(scroll_layer_id);
+}
+
+void LayerTreeHostImpl::UnregisterScrollElasticityHelper(int scroll_layer_id) {
+  scroll_elasticity_helpers_.erase(scroll_layer_id);
+}
+
+ScrollElasticityHelper* LayerTreeHostImpl::ScrollElasticityHelperForId(
+    int scroll_layer_id) {
+  if (!settings().enable_elastic_overscroll)
+    return nullptr;
+
+  auto i = scroll_elasticity_helpers_.find(scroll_layer_id);
+  if (i != scroll_elasticity_helpers_.end())
+    return i->second.get();
+
+  if (!root_scroll_elasticity_helper_) {
+    root_scroll_elasticity_helper_.reset(
+        ScrollElasticityHelper::CreateForLayerTreeHostImpl(this));
+  }
+  return root_scroll_elasticity_helper_.get();
+}
+
 void LayerTreeHostImpl::PostDelayedScrollbarAnimationTask(
     const base::Closure& task,
     base::TimeDelta delay) {