Plumb smooth scrolling in Chromium compositor

ui/events/gestures/blink/web_gesture_curve_impl.cc

Index: ui/events/gestures/blink/web_gesture_curve_impl.cc
diff --git a/ui/events/gestures/blink/web_gesture_curve_impl.cc b/ui/events/gestures/blink/web_gesture_curve_impl.cc
index 96cebee462f2c012b0d88505628f3b2c6e575e5b..9eda4ff69f1ea6dfd7c26acd515b6a19343bd16d 100644
--- a/ui/events/gestures/blink/web_gesture_curve_impl.cc
+++ b/ui/events/gestures/blink/web_gesture_curve_impl.cc
@@ -42,6 +42,26 @@ scoped_ptr<GestureCurve> CreateDefaultPlatformCurve(
 #endif
 }
 
+scoped_ptr<GestureCurve> CreateSmoothScrollingCurve(float start_x,
+                                                    float start_y,
+                                                    float dx,
+                                                    float dy,
+                                                    base::TimeDelta duration) {
+  DCHECK(duration > base::TimeDelta());
+#if defined(OS_ANDROID)
+  auto scroller = make_scoped_ptr(new Scroller(Scroller::Config()));
+  base::TimeTicks start_time = base::TimeTicks();
+
+  scroller->StartScroll(start_x, start_y, dx, dy, start_time, duration);
+  return scroller.Pass();
+#else
+  float vx = dx / duration.InSecondsF();

[jdduke (slow), 2015/07/23 15:32:50]

I'd almost rather we NOTREACHED() here and return nullptr so other platforms
don't inadvertently think this will do smooth scrolling. In theory Scroller's
smooth scrolling would work just fine for other platfoms, but for now I'd prefer
we just not support the path until we need to.

+  float vy = dy / duration.InSecondsF();
+  return make_scoped_ptr(
+      new FlingCurve(gfx::Vector2dF(vx, vy), base::TimeTicks()));
+#endif
+}
+
 }  // namespace
 
 // static
@@ -55,6 +75,20 @@ scoped_ptr<WebGestureCurve> WebGestureCurveImpl::CreateFromDefaultPlatformCurve(
 }
 
 // static
+scoped_ptr<WebGestureCurve> WebGestureCurveImpl::CreateFromSmoothScrollingCurve(
+    float start_x,
+    float start_y,
+    float dx,
+    float dy,
+    base::TimeDelta duration,
+    bool on_main_thread) {
+  const gfx::Vector2dF initial_offset(start_x, start_y);
+  return scoped_ptr<WebGestureCurve>(new WebGestureCurveImpl(
+      CreateSmoothScrollingCurve(start_x, start_y, dx, dy, duration),
+      initial_offset, on_main_thread ? ThreadType::MAIN : ThreadType::IMPL));
+}
+
+// static
 scoped_ptr<WebGestureCurve> WebGestureCurveImpl::CreateFromUICurveForTesting(
     scoped_ptr<GestureCurve> curve,
     const gfx::Vector2dF& initial_offset) {