Move overscroll bounce to impl thread

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 77c484fd1a4a6bef187c2bec963533ec8a750c4f..08b0ad143c64556b96b609750aca5d3502faf9fd 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -67,6 +67,7 @@
 #include "cc/trees/layer_tree_impl.h"
 #include "cc/trees/occlusion_tracker.h"
 #include "cc/trees/single_thread_proxy.h"
+#include "cc/trees/tree_scroll_elasticity_client.h"
 #include "cc/trees/tree_synchronizer.h"
 #include "gpu/command_buffer/client/gles2_interface.h"
 #include "gpu/GLES2/gl2extchromium.h"
@@ -278,6 +279,8 @@ LayerTreeHostImpl::LayerTreeHostImpl(
       wheel_scrolling_(false),
       scroll_affects_scroll_handler_(false),
       scroll_layer_id_when_mouse_over_scrollbar_(0),
+      scroll_elasticity_client_(
+          new TreeScrollElasticityClient(this)),
       tile_priorities_dirty_(false),
       root_layer_scroll_offset_delegate_(NULL),
       settings_(settings),
@@ -459,6 +462,10 @@ bool LayerTreeHostImpl::CanDraw() const {
 void LayerTreeHostImpl::Animate(base::TimeTicks monotonic_time) {
   if (input_handler_client_)
     input_handler_client_->Animate(monotonic_time);
+  if (scroll_elasticity_client_->controller()) {
+    scroll_elasticity_client_->controller()->Animate(
+        monotonic_time);
+  }
   AnimatePageScale(monotonic_time);
   AnimateLayers(monotonic_time);
   AnimateScrollbars(monotonic_time);
@@ -515,6 +522,11 @@ LayerTreeHostImpl::CreateLatencyInfoSwapPromiseMonitor(
       new LatencyInfoSwapPromiseMonitor(latency, NULL, this));
 }
 
+ScrollElasticityControllerClient*
+    LayerTreeHostImpl::GetScrollElasticityControllerClient() {
+  return scroll_elasticity_client_.get();
+}
+
 void LayerTreeHostImpl::QueueSwapPromiseForMainThreadScrollUpdate(
     scoped_ptr<SwapPromise> swap_promise) {
   swap_promises_for_main_thread_scroll_update_.push_back(swap_promise.Pass());