Fix scrollbars missing after lost context

cc/test/fake_scrollbar_layer.cc

Index: cc/test/fake_scrollbar_layer.cc
diff --git a/cc/test/fake_scrollbar_layer.cc b/cc/test/fake_scrollbar_layer.cc
index d6e5f0a1b43fb2995fd68b88b923fc9a80d3d877..96c9daff311b098ff76686a2f8dced570886c04a 100644
--- a/cc/test/fake_scrollbar_layer.cc
+++ b/cc/test/fake_scrollbar_layer.cc
@@ -4,6 +4,7 @@
 
 #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"
@@ -19,7 +20,9 @@ FakeScrollbarLayer::FakeScrollbarLayer(
         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);
@@ -31,8 +34,12 @@ 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