cc: Make impl-thread property trees handle fixed-position layers

cc/layers/layer_impl.cc

 // Copyright 2012 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 "cc/layers/layer_impl.h"
 
 #include "base/json/json_reader.h"
 #include "base/strings/stringprintf.h"
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_argument.h"
@@ skipping 1198 matching lines @@
   if (IsActive())
     return gfx::Vector2dF(scroll_offset_->Delta().x(),
                           scroll_offset_->Delta().y());
   else
     return gfx::Vector2dF(scroll_offset_->PendingDelta().get().x(),
                           scroll_offset_->PendingDelta().get().y());
 }
 
 void LayerImpl::SetScrollDelta(const gfx::Vector2dF& delta) {
   DCHECK(IsActive());
+  DCHECK(scrollable() || delta.IsZero());
   SetCurrentScrollOffset(scroll_offset_->ActiveBase() +
                          gfx::ScrollOffset(delta));
 }
 
 gfx::ScrollOffset LayerImpl::BaseScrollOffset() const {
   if (IsActive())
     return scroll_offset_->ActiveBase();
   else
     return scroll_offset_->PendingBase();
 }
@@ skipping 452 matching lines @@
   gfx::Transform scaled_draw_transform =
       draw_properties_.target_space_transform;
   scaled_draw_transform.Scale(SK_MScalar1 / scale, SK_MScalar1 / scale);
   gfx::Size scaled_content_bounds =
       gfx::ToCeiledSize(gfx::ScaleSize(content_bounds(), scale));
   return MathUtil::MapEnclosingClippedRect(scaled_draw_transform,
                                            gfx::Rect(scaled_content_bounds));
 }
 
 }  // namespace cc