Move viewport scrolling logic into separate class

cc/layers/viewport.h

Index: cc/layers/viewport.h
diff --git a/cc/layers/viewport.h b/cc/layers/viewport.h
new file mode 100644
index 0000000000000000000000000000000000000000..f552b8270c9d347cef5ed4ed517d763e0ca1f728
--- /dev/null
+++ b/cc/layers/viewport.h
@@ -0,0 +1,63 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.

[aelias_OOO_until_Jul13, 2015/03/25 19:56:07]

Nit: 2015

[bokan, 2015/03/25 20:38:34]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CC_LAYERS_VIEWPORT_H_
+#define CC_LAYERS_VIEWPORT_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"

[aelias_OOO_until_Jul13, 2015/03/25 19:56:07]

This looks unused, please delete

[bokan, 2015/03/25 20:38:35]

Done.

+#include "cc/layers/layer_impl.h"
+#include "ui/gfx/geometry/size.h"

[aelias_OOO_until_Jul13, 2015/03/25 19:56:07]

This looks unused, please delete

[bokan, 2015/03/25 20:38:35]

Done.

+#include "ui/gfx/geometry/vector2d_f.h"
+
+namespace cc {
+
+class LayerTreeHostImpl;
+
+// Encapsulates the Layers that comprise the viewport. The "viewport" is made up

[aelias_OOO_until_Jul13, 2015/03/25 19:56:07]

It would be more accurate to write "Encapsulates gesture handling logic on the
layers"

[bokan, 2015/03/25 20:38:35]

Done.

+// of two layers, the inner viewport (visual) and the outer viewport (layout).
+// These layers have different scroll bubbling behavior from the rest of the
+// layer tree which is encoded in this class.
+class CC_EXPORT Viewport {
+ public:
+  struct ScrollResult {
+    ScrollResult() : did_scroll_top_controls(false) {}
+    gfx::Vector2dF applied_delta;
+    gfx::Vector2dF unused_scroll_delta;
+    bool did_scroll_top_controls;

[aelias_OOO_until_Jul13, 2015/03/25 19:56:07]

I think in this struct, it would be more natural to contain the amount that the
top controls was scrolled.  Then the caller in LTHI is free to only make use of
whether it's != 0 for now.

[bokan, 2015/03/25 20:38:35]

Done.

+  };
+
+  static scoped_ptr<Viewport> Create(LayerTreeHostImpl* host_impl);
+
+  // Scrolls the viewport, applying the unique bubbling between the inner and
+  // outer viewport. Scrolls can be consumed by top controls.
+  ScrollResult ScrollBy(const gfx::Vector2dF& delta,
+                          const gfx::Point& viewport_point,

[aelias_OOO_until_Jul13, 2015/03/25 19:56:07]

Indent wrong, please run "git cl format"

[bokan, 2015/03/25 20:38:35]

It seems to do nothing for me, maybe because I've already committed...Done
manually though.

+                          bool is_wheel_scroll);
+
+ private:
+  explicit Viewport(LayerTreeHostImpl* host_impl);
+
+  bool ShouldTopControlsConsumeScroll(const gfx::Vector2dF& scroll_delta) const;
+  gfx::Vector2dF AdjustOverscroll(const gfx::Vector2dF& delta) const;
+
+  // Sends the delta to the top controls, returns the amount applied.
+  gfx::Vector2dF ScrollTopControls(const gfx::Vector2dF& delta);
+
+  gfx::ScrollOffset MaxTotalScrollOffset() const;
+  gfx::ScrollOffset TotalScrollOffset() const;
+
+  LayerImpl* InnerScrollLayer() const;
+  LayerImpl* OuterScrollLayer() const;
+
+  LayerTreeHostImpl* host_impl_;
+  LayerImpl* inner_scroll_layer_;

[aelias_OOO_until_Jul13, 2015/03/25 19:56:07]

Looks like you deleted all use of these but not the fields themselves.

[bokan, 2015/03/25 20:38:35]

Done.

+  LayerImpl* outer_scroll_layer_;
+
+  DISALLOW_COPY_AND_ASSIGN(Viewport);
+};
+
+}  // namespace cc
+
+#endif  // CC_LAYERS_VIEWPORT_H_