Fix scrollbars missing after lost context

cc/test/fake_scrollbar_layer.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/test/fake_scrollbar_layer.h"
 
+#include "cc/resource_update_queue.h"
 #include "cc/test/fake_scrollbar_theme_painter.h"
 #include "cc/test/fake_web_scrollbar.h"
 #include "cc/test/fake_web_scrollbar_theme_geometry.h"
 
 namespace cc {
 
 FakeScrollbarLayer::FakeScrollbarLayer(
     bool paint_during_update, bool has_thumb, int scrolling_layer_id)
     : ScrollbarLayer(
         FakeWebScrollbar::create().PassAs<WebKit::WebScrollbar>(),
         FakeScrollbarThemePainter::Create(paint_during_update)
         .PassAs<ScrollbarThemePainter>(),
         FakeWebScrollbarThemeGeometry::create(has_thumb)
         .PassAs<WebKit::WebScrollbarThemeGeometry>(),
         scrolling_layer_id),
-      update_count_(0) {
+      update_count_(0),
+      last_update_full_upload_size_(0),
+      last_update_partial_upload_size_(0) {
   setAnchorPoint(gfx::PointF(0, 0));
   setBounds(gfx::Size(1, 1));
   setIsDrawable(true);
 }
 
 FakeScrollbarLayer::~FakeScrollbarLayer() {}
 
 void FakeScrollbarLayer::update(
     ResourceUpdateQueue& queue,
     const OcclusionTracker* occlusion,
     RenderingStats& stats) {
+  size_t full = queue.fullUploadSize();
+  size_t partial = queue.partialUploadSize();
   ScrollbarLayer::update(queue, occlusion, stats);
   update_count_++;
+  last_update_full_upload_size_ = queue.fullUploadSize() - full;
+  last_update_partial_upload_size_ = queue.partialUploadSize() - partial;
 }
 
 }  // namespace cc