Overscroll and Elasticity for views::ScrollView

cc/input/scroll_elasticity_helper.cc

Index: cc/input/scroll_elasticity_helper.cc
diff --git a/cc/input/scroll_elasticity_helper.cc b/cc/input/scroll_elasticity_helper.cc
index 413d64f6bf9b285a35e599e39f5aa0fb4cb28700..901f8b242ddd3475ff57f1aa996b08ed0d6a0325 100644
--- a/cc/input/scroll_elasticity_helper.cc
+++ b/cc/input/scroll_elasticity_helper.cc
@@ -4,11 +4,14 @@
 
 #include "cc/input/scroll_elasticity_helper.h"
 
+#include "base/macros.h"
+#include "base/memory/ptr_util.h"
 #include "cc/layers/layer_impl.h"
 #include "cc/trees/layer_tree_host_impl.h"
 #include "cc/trees/layer_tree_impl.h"
 
 namespace cc {
+namespace {
 
 class ScrollElasticityHelperImpl : public ScrollElasticityHelper {
  public:
@@ -23,14 +26,21 @@ class ScrollElasticityHelperImpl : public ScrollElasticityHelper {
   void ScrollBy(const gfx::Vector2dF& delta) override;
   void RequestOneBeginFrame() override;
 
+  base::WeakPtr<ScrollElasticityHelper> GetWeakPtr() override {
+    return weak_ptr_factory_.GetWeakPtr();
+  }
+
  private:
   LayerTreeHostImpl* layer_tree_host_impl_;
+
+  base::WeakPtrFactory<ScrollElasticityHelperImpl> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScrollElasticityHelperImpl);
 };
 
 ScrollElasticityHelperImpl::ScrollElasticityHelperImpl(
     LayerTreeHostImpl* layer_tree)
-    : layer_tree_host_impl_(layer_tree) {
-}
+    : layer_tree_host_impl_(layer_tree), weak_ptr_factory_(this) {}
 
 ScrollElasticityHelperImpl::~ScrollElasticityHelperImpl() {
 }
@@ -82,6 +92,99 @@ void ScrollElasticityHelperImpl::RequestOneBeginFrame() {
   layer_tree_host_impl_->SetNeedsOneBeginImplFrame();
 }
 
+class LayerScrollElasticityHelperImpl : public ScrollElasticityHelper {
+ public:
+  LayerScrollElasticityHelperImpl(int layer_scroll_layer_id,
+                                  LayerTreeHostImpl* layer_tree_host_impl);
+
+  bool IsUserScrollable() const override;
+  gfx::Vector2dF StretchAmount() const override;
+  void SetStretchAmount(const gfx::Vector2dF& stretch_amount) override;
+  gfx::ScrollOffset ScrollOffset() const override;
+  gfx::ScrollOffset MaxScrollOffset() const override;
+  void ScrollBy(const gfx::Vector2dF& delta) override;
+  void RequestOneBeginFrame() override;
+
+  base::WeakPtr<ScrollElasticityHelper> GetWeakPtr() override {
+    return weak_ptr_factory_.GetWeakPtr();
+  }
+
+ private:
+  LayerImpl* layer() const;
+
+  LayerTreeHostImpl* layer_tree_host_impl_;
+  int layer_scroll_layer_id_;
+
+  base::WeakPtrFactory<LayerScrollElasticityHelperImpl> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(LayerScrollElasticityHelperImpl);
+};
+
+LayerScrollElasticityHelperImpl::LayerScrollElasticityHelperImpl(
+    int layer_scroll_layer_id,
+    LayerTreeHostImpl* layer_tree_host_impl)
+    : layer_tree_host_impl_(layer_tree_host_impl),
+      layer_scroll_layer_id_(layer_scroll_layer_id),
+      weak_ptr_factory_(this) {}
+
+bool LayerScrollElasticityHelperImpl::IsUserScrollable() const {
+  // LayerTreeHostImpl wouldn't have created |this| in the first place if the
+  // layer wasn't user-scrollable.
+  return true;
+}
+
+gfx::Vector2dF LayerScrollElasticityHelperImpl::StretchAmount() const {
+  return ScrollOffsetToVector2dF(layer()->CurrentOverscroll());
+}
+
+void LayerScrollElasticityHelperImpl::SetStretchAmount(
+    const gfx::Vector2dF& stretch_amount) {
+  if (stretch_amount == StretchAmount())
+    return;
+
+  layer()->SetCurrentOverscroll(gfx::ScrollOffset(stretch_amount));
+
+  // For now, also inform the LayerTreeImpl of the stretch amount. This will
+  // then get redistributed over the scrolling layer.
+  // TODO(tapted): Remove this - it shouldn't be necessary.
+  layer_tree_host_impl_->active_tree()->elastic_overscroll()->SetCurrent(
+      stretch_amount);
+  layer_tree_host_impl_->SetNeedsCommit();
+}
+
+gfx::ScrollOffset LayerScrollElasticityHelperImpl::ScrollOffset() const {
+  return layer()->CurrentScrollOffset();
+}
+
+gfx::ScrollOffset LayerScrollElasticityHelperImpl::MaxScrollOffset() const {
+  return layer()->MaxScrollOffset();
+}
+
+void LayerScrollElasticityHelperImpl::ScrollBy(const gfx::Vector2dF& delta) {
+  layer()->ScrollBy(delta);
+}
+
+void LayerScrollElasticityHelperImpl::RequestOneBeginFrame() {
+  layer_tree_host_impl_->SetNeedsOneBeginImplFrame();
+}
+
+LayerImpl* LayerScrollElasticityHelperImpl::layer() const {
+  LayerImpl* scrolling_layer =
+      layer_tree_host_impl_->active_tree()->FindActiveTreeLayerById(
+          layer_scroll_layer_id_);
+  return scrolling_layer;
+}
+
+}  // namespace
+
+// static
+std::unique_ptr<ScrollElasticityHelper> ScrollElasticityHelper::CreateForLayer(
+    int layer_scroll_layer_id,
+    LayerTreeHostImpl* layer_tree_host_impl) {
+  return base::MakeUnique<LayerScrollElasticityHelperImpl>(
+      layer_scroll_layer_id, layer_tree_host_impl);
+}
+
 // static
 ScrollElasticityHelper* ScrollElasticityHelper::CreateForLayerTreeHostImpl(
     LayerTreeHostImpl* layer_tree_host_impl) {