Make it possible to delegate root layer scroll offset outside of cc.

This change makes it possible for the embedder to own the root layer
scroll offset.

BUG=b/6029133

Review URL: https://chromiumcodereview.appspot.com/13869006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@197178 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 50 insertions, 0 deletions

diff --git a/cc/input/input_handler.h b/cc/input/input_handler.h
index 982befa..b3f805e 100644
--- a/cc/input/input_handler.h
+++ b/cc/input/input_handler.h
@@ -19,6 +19,8 @@ class Vector2dF;
 
 namespace cc {
 
+class LayerScrollOffsetDelegate;
+
 // The InputHandler is a way for the embedders to interact with the impl thread
 // side of the compositor implementation. There is one InputHandler per
 // LayerTreeHost. To use the input handler, implement the InputHanderClient
@@ -62,6 +64,16 @@ class CC_EXPORT InputHandler {
   // returned ScrollStarted.
   virtual void ScrollEnd() = 0;
 
+  virtual void SetRootLayerScrollOffsetDelegate(
+      LayerScrollOffsetDelegate* root_layer_scroll_offset_delegate) = 0;
+
+  // Called when the value returned by
+  // LayerScrollOffsetDelegate.GetTotalScrollOffset has changed for reasons
+  // other than a SetTotalScrollOffset call.
+  // NOTE: This should only called after a valid delegate was set via a call to
+  // SetRootLayerScrollOffsetDelegate.
+  virtual void OnRootLayerDelegatedScrollOffsetChanged() = 0;
+
   virtual void PinchGestureBegin() = 0;
   virtual void PinchGestureUpdate(float magnify_delta, gfx::Point anchor) = 0;
   virtual void PinchGestureEnd() = 0;
diff --git a/cc/input/layer_scroll_offset_delegate.h b/cc/input/layer_scroll_offset_delegate.h
new file mode 100644
index 0000000..1431a80
--- /dev/null
+++ b/cc/input/layer_scroll_offset_delegate.h
@@ -0,0 +1,38 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CC_INPUT_LAYER_SCROLL_OFFSET_DELEGATE_H_
+#define CC_INPUT_LAYER_SCROLL_OFFSET_DELEGATE_H_
+
+namespace cc {
+
+// The LayerScrollOffsetDelegate allows for the embedder to take ownership of
+// the scroll offset of the root layer.
+//
+// The LayerScrollOffsetDelegate is only used on the impl thread.
+class LayerScrollOffsetDelegate {
+ public:
+  // This is called by the compositor when the scroll offset of the layer would
+  // have otherwise changed.
+  virtual void SetTotalScrollOffset(gfx::Vector2dF new_value) = 0;
+
+  // This is called by the compositor to query the current scroll offset of the
+  // layer.
+  // There is no requirement that the return values of this method are
+  // stable in time (two subsequent calls may yield different results).
+  // The return value is not required to be related to the values passed in to
+  // the SetTotalScrollOffset method in any way.
+  virtual gfx::Vector2dF GetTotalScrollOffset() = 0;
+
+ protected:
+  LayerScrollOffsetDelegate() {}
+  virtual ~LayerScrollOffsetDelegate() {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(LayerScrollOffsetDelegate);
+};
+
+}  // namespace cc
+
+#endif  // CC_INPUT_LAYER_SCROLL_OFFSET_DELEGATE_H_