Adding momentum/overscroll to views:: ScrollViews

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index 1c3f3bc0e1256c0f734c25c32661214c9ce02073..0677baf840994ce8cfc1d6fc0a64ef3f1467e32b 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -38,6 +38,7 @@
 #include "ui/compositor/dip_util.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/layer_animator_collection.h"
+#include "ui/compositor/overscroll/ui_scroll_input_manager.h"
 #include "ui/gl/gl_context.h"
 #include "ui/gl/gl_switches.h"
 
@@ -102,6 +103,10 @@ Compositor::Compositor(ui::ContextFactory* context_factory,
 
   cc::LayerTreeSettings settings;
 
+#if defined(OS_MACOSX)
+  settings.enable_elastic_overscroll = true;
+#endif
+
   // This will ensure PictureLayers always can have LCD text, to match the
   // previous behaviour with ContentLayers, where LCD-not-allowed notifications
   // were ignored.
@@ -209,6 +214,14 @@ Compositor::Compositor(ui::ContextFactory* context_factory,
   params.main_task_runner = task_runner_;
   params.animation_host = cc::AnimationHost::CreateMainInstance();
   host_ = cc::LayerTreeHost::CreateSingleThreaded(this, &params);
+
+  // Tie composited scrolling with whether the platform wants elastic scrolling.
+  // TODO(tapted): Use composited scrolling on all platforms.
+  if (settings.enable_elastic_overscroll) {
+    scroll_input_manager_.reset(
+        new UIScrollInputManager(host_->GetInputHandler()));
+  }
+
   UMA_HISTOGRAM_TIMES("GPU.CreateBrowserCompositor",
                       base::TimeTicks::Now() - before_create);
 
@@ -502,6 +515,10 @@ scoped_refptr<CompositorLock> Compositor::GetCompositorLock() {
   return compositor_lock_;
 }
 
+bool Compositor::ScrollLayerTo(int layer_id, const gfx::ScrollOffset& offset) {
+  return host_->GetInputHandler()->ScrollLayerTo(layer_id, offset);
+}
+
 void Compositor::UnlockCompositor() {
   DCHECK(compositor_lock_);
   compositor_lock_ = NULL;