Delegate root layer scroll offset to android_webview.

content/renderer/android/synchronous_compositor_impl.h

+// 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 CONTENT_RENDERER_ANDROID_SYNCHRONOUS_COMPOSITOR_IMPL_H_
+#define CONTENT_RENDERER_ANDROID_SYNCHRONOUS_COMPOSITOR_IMPL_H_
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "base/memory/scoped_ptr.h"
+#include "cc/input/layer_scroll_offset_delegate.h"
+#include "content/public/renderer/android/synchronous_compositor.h"
+#include "content/renderer/android/synchronous_compositor_output_surface.h"
+
+namespace cc {
+class InputHandlerClient;
+class OutputSurface;
+}
+
+namespace content {
+
+// Specialization of the output surface that adapts it to implement the

[joth, 2013/05/16 18:21:42]

comment doesn't apply here -- needs rewriting
include a bit about ownership model of this class. (cc owns the OutputSurface,
does it also own this class? etc)

+// content::SynchronousCompositor public API. This class effects an "inversion
+// of control" - enabling drawing to be  orchestrated by the embedding
+// layer, instead of driven by the compositor internals - hence it holds two
+// 'client' pointers (including |client_| in the OutputSurface baseclass) which
+// represent the consumers of the two roles in plays.
+// This class can be created only on the main thread, but then becomes pinned
+// to a fixed thread when BindToClient is called.
+class SynchronousCompositorImpl
+    : public SynchronousCompositor,
+      public SynchronousCompositorOutputSurface::Delegate,
+      private cc::LayerScrollOffsetDelegate {
+ public:
+  explicit SynchronousCompositorImpl(int32 routing_id);
+  virtual ~SynchronousCompositorImpl();
+
+  scoped_ptr<cc::OutputSurface> CreateOutputSurface();
+  scoped_ptr<cc::InputHandlerClient> CreateInputHandlerClientWrapper(
+      scoped_ptr<cc::InputHandlerClient> wraped_client);
+
+  // SynchronousCompositor.
+  virtual bool IsHwReady() OVERRIDE;
+  virtual void SetClient(SynchronousCompositorClient* compositor_client)
+      OVERRIDE;
+  virtual bool DemandDrawSw(SkCanvas* canvas) OVERRIDE;
+  virtual bool DemandDrawHw(
+      gfx::Size view_size,
+      const gfx::Transform& transform,
+      gfx::Rect clip) OVERRIDE;
+
+  // SynchronousCompositorOutputSurface::Delegate
+  virtual void SetContinuousInvalidate(bool enable) OVERRIDE;
+  virtual void DidCreateSynchronousCompositor() OVERRIDE;
+  virtual void DidDestroyCompositor() OVERRIDE;
+
+ private:
+  bool CalledOnValidThread() const;
+
+  // LayerScrollOffsetDelegate
+  virtual void SetTotalScrollOffset(gfx::Vector2dF new_value) OVERRIDE;
+  virtual gfx::Vector2dF GetTotalScrollOffset() OVERRIDE;
+
+  int routing_id_;
+  SynchronousCompositorClient* compositor_client_;
+  SynchronousCompositorOutputSurface* output_surface_;
+
+  DISALLOW_COPY_AND_ASSIGN(SynchronousCompositorImpl);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_ANDROID_SYNCHRONOUS_COMPOSITOR_IMPL_H_