Unify Android Webview and Chrome's fling

cc/input/layer_scroll_offset_delegate.h

Index: cc/input/layer_scroll_offset_delegate.h
diff --git a/cc/input/layer_scroll_offset_delegate.h b/cc/input/layer_scroll_offset_delegate.h
index 02ba011118dfb5621bf3a53c482b8ae8c1a40e67..e0297190a8e49149f474560f43b68ebc7c27a7b1 100644
--- a/cc/input/layer_scroll_offset_delegate.h
+++ b/cc/input/layer_scroll_offset_delegate.h
@@ -6,6 +6,8 @@
 #define CC_INPUT_LAYER_SCROLL_OFFSET_DELEGATE_H_
 
 #include "base/basictypes.h"
+#include "base/callback_forward.h"
+#include "base/time/time.h"
 #include "ui/gfx/geometry/scroll_offset.h"
 #include "ui/gfx/geometry/size_f.h"
 
@@ -44,7 +46,13 @@ class LayerScrollOffsetDelegate {
 
   // This is called by the compositor to check whether a delegate-managed fling
   // is active or not.
-  virtual bool IsExternalFlingActive() const = 0;
+  // TODO(jdduke): Remove?

[aelias_OOO_until_Jul13, 2015/05/09 03:32:05]

Seems we can't yet because of the other smooth scrolls, is that right?

[hush (inactive), 2015/05/12 19:08:45]

Right. We will still need to keep it until we can unify smooth scrolls with
Chrome. I will upload a followup CL after this CL is submitted.
Jared and I had a very brief discussion about how to unify smooth scrolls a
while back.
The high level plan for that is we will introduce 2 new gesture events on
ContentViewCore(maybe call them SmoothScrollStart/Cancel), do the plumbing up
until web_gesture_curve_impl.cc to expose Scroller::startScroll.

+  virtual bool IsExternalScrollActive() const = 0;
+
+  // This is called by the compositor when a fling hitting the root layer
+  // requires a scheduled animation update.
+  typedef base::Callback<void(base::TimeTicks)> AnimationCallback;
+  virtual void SetNeedsAnimate(const AnimationCallback& animation) = 0;
 
  protected:
   LayerScrollOffsetDelegate() {}