Hook ScrollElasticityController to InputHandlerProxy

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 b797c1c96963d761622d6a32b841d68ea1a25712..ecc4dfdbf0d16df4b7067ba48960e120f2a3c6e4 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -29,6 +29,7 @@
 #include "cc/debug/rendering_stats_instrumentation.h"
 #include "cc/debug/traced_value.h"
 #include "cc/input/page_scale_animation.h"
+#include "cc/input/scroll_elasticity_helper.h"
 #include "cc/input/top_controls_manager.h"
 #include "cc/layers/append_quads_data.h"
 #include "cc/layers/heads_up_display_layer_impl.h"
@@ -281,6 +282,8 @@ LayerTreeHostImpl::~LayerTreeHostImpl() {
     input_handler_client_->WillShutdown();
     input_handler_client_ = NULL;
   }
+  if (scroll_elasticity_helper_)
+    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 registrar
@@ -450,6 +453,12 @@ LayerTreeHostImpl::CreateLatencyInfoSwapPromiseMonitor(
       new LatencyInfoSwapPromiseMonitor(latency, NULL, this));
 }
 
+ScrollElasticityHelper* LayerTreeHostImpl::CreateScrollElasticityHelper() {
+  DCHECK(!scroll_elasticity_helper_);
+  scroll_elasticity_helper_.reset(new ScrollElasticityHelper(this));
+  return scroll_elasticity_helper_.get();
+}
+
 void LayerTreeHostImpl::QueueSwapPromiseForMainThreadScrollUpdate(
     scoped_ptr<SwapPromise> swap_promise) {
   swap_promises_for_main_thread_scroll_update_.push_back(swap_promise.Pass());