Delegate root layer scroll offset to android_webview.

content/renderer/android/synchronous_compositor_impl.cc

 // 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.
 
 #include "content/renderer/android/synchronous_compositor_impl.h"
 
 #include "base/message_loop.h"
 #include "cc/input/input_handler.h"
 #include "content/public/renderer/android/synchronous_compositor_client.h"
 #include "content/public/renderer/content_renderer_client.h"
 
 namespace content {
 
 SynchronousCompositorImpl::SynchronousCompositorImpl(int32 routing_id)
-    : routing_id_(routing_id), compositor_client_(NULL) {}
+    : routing_id_(routing_id), compositor_client_(NULL) {
+}
 
 SynchronousCompositorImpl::~SynchronousCompositorImpl() {
 }
 
 scoped_ptr<cc::OutputSurface>
 SynchronousCompositorImpl::CreateOutputSurface() {
   scoped_ptr<SynchronousCompositorOutputSurface> output_surface(
       new SynchronousCompositorOutputSurface(this));
   output_surface_ = output_surface.get();
   return output_surface.PassAs<cc::OutputSurface>();
@@ skipping 24 matching lines @@
       const gfx::Transform& transform,
       gfx::Rect damage_area) {
   DCHECK(CalledOnValidThread());
   DCHECK(output_surface_);
 
   return output_surface_->DemandDrawHw(view_size, transform, damage_area);
 }
 
 void SynchronousCompositorImpl::SetContinuousInvalidate(bool enable) {
   DCHECK(CalledOnValidThread());
-  // compositor_client_ can be NULL during WebContents teardown.
   if (compositor_client_)
     compositor_client_->SetContinuousInvalidate(enable);
 }
 
 void SynchronousCompositorImpl::DidCreateSynchronousOutputSurface() {
   DCHECK(CalledOnValidThread());
   GetContentClient()->renderer()->DidCreateSynchronousCompositor(routing_id_,
                                                                  this);
 }
 
 void SynchronousCompositorImpl::DidDestroySynchronousOutputSurface() {
   DCHECK(CalledOnValidThread());
   output_surface_ = NULL;
-  // compositor_client_ can be NULL during WebContents teardown.
   if (compositor_client_)
     compositor_client_->DidDestroyCompositor(this);
 }
 
+void SynchronousCompositorImpl::SetTotalScrollOffset(gfx::Vector2dF new_value) {
+  DCHECK(CalledOnValidThread());
+  if (compositor_client_)
+    compositor_client_->SetTotalRootLayerScrollOffset(new_value);
+}
+
+gfx::Vector2dF SynchronousCompositorImpl::GetTotalScrollOffset() {
+  DCHECK(CalledOnValidThread());
+  if (compositor_client_)
+    return compositor_client_->GetTotalRootLayerScrollOffset();
+  else
+    return gfx::Vector2dF();

[mkosiba (inactive), 2013/05/29 13:18:24]

this is the only downside of checking for compositor_client_ (instead of
removing the scroll offset delegate ). If the compositor_client_ can only be
NULL during setup/teardown then this is fine, but otherwise this could lead to
the page scroll jumping to the top at seemingly arbitrary times.

+}
+
 // Not using base::NonThreadSafe as we want to enforce a more exacting threading
 // requirement: SynchronousCompositorImpl() must only be used by
 // embedders that supply their own compositor loop via
 // OverrideCompositorMessageLoop().
 bool SynchronousCompositorImpl::CalledOnValidThread() const {
   return base::MessageLoop::current() && (base::MessageLoop::current() ==
       GetContentClient()->renderer()->OverrideCompositorMessageLoop());
 }
 
 }  // namespace content