Connect LTHI::ScrollAnimated to cc::Viewport

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index a7d6b083235eca111337803d8af04cf9f367e3e1..dbdee2ce1d60e4c87e8a8c5eed67a9f2ddcc1486 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -536,6 +536,18 @@ class CC_EXPORT LayerTreeHostImpl
     bool opaque;
   };
 
+  struct ScrollAmount {

[bokan, 2016/04/06 13:35:52]

I don't like this, there's opportunity for delta and target_offset to point to
different locations and it makes it harder to think about how things will work
given a ScrollAmount. Why not just use a delta and convert to an offset using
clamp(current_offset + delta)?

[ymalik, 2016/04/06 15:33:45]

You're right, it's not used often enough to justify. Done!

+    ScrollAmount(gfx::Vector2dF delta, gfx::ScrollOffset offset)
+        : delta(delta), target_offset(offset) {}
+    gfx::Vector2dF delta;
+    gfx::ScrollOffset target_offset;
+  };
+
+  // Returns the amount of delta that can be applied to scroll_node, taking
+  // page scale into account.
+  ScrollAmount ComputeScrollDelta(ScrollNode* scroll_node,
+                                  const gfx::Vector2dF& delta);
+
   void ScheduleMicroBenchmark(scoped_ptr<MicroBenchmarkImpl> benchmark);
 
   CompositorFrameMetadata MakeCompositorFrameMetadata() const;
@@ -616,6 +628,11 @@ class CC_EXPORT LayerTreeHostImpl
                                        const ScrollTree& scroll_tree,
                                        ScrollNode* scroll_node) const;
 
+  // Returns true if a scroll offset animation is created and false if we scroll
+  // by the desired amount without an animation.
+  bool ScrollAnimationCreate(ScrollNode* scroll_node,
+                             const ScrollAmount& scroll_amount);
+
  protected:
   LayerTreeHostImpl(
       const LayerTreeSettings& settings,
@@ -714,9 +731,6 @@ class CC_EXPORT LayerTreeHostImpl
 
   void ScrollAnimationAbort(LayerImpl* layer_impl);
 
-  void ScrollAnimationCreate(ScrollNode* scroll_node,
-                             const gfx::ScrollOffset& target_offset,
-                             const gfx::ScrollOffset& current_offset);
   bool ScrollAnimationUpdateTarget(ScrollNode* scroll_node,
                                    const gfx::Vector2dF& scroll_delta);