[not for review - epic CL] Adding Elastic+Momentum+Layered scrolling to views::ScrollView

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index 846bab0d17c68c871055b30d3ff19bffd2fdae1c..00ccce42f3b95946344555d230ca7076c73d42fa 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_switches.h"
 
 namespace {
@@ -101,6 +102,10 @@ 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.
@@ -208,6 +213,14 @@ 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);
 
@@ -385,6 +398,14 @@ bool Compositor::IsVisible() {
   return host_->visible();
 }
 
+bool Compositor::ScrollLayerTo(int layer_id, const gfx::ScrollOffset& offset) {
+  return host_->GetInputHandler()->ScrollLayerTo(layer_id, offset);
+}
+
+gfx::ScrollOffset Compositor::GetScrollOffsetForLayer(int layer_id) const {
+  return host_->GetInputHandler()->GetScrollOffsetForLayer(layer_id);
+}
+
 void Compositor::SetAuthoritativeVSyncInterval(
     const base::TimeDelta& interval) {
   context_factory_->SetAuthoritativeVSyncInterval(this, interval);