Clean LayerImpl's scroll offset callers in unit tests.

cc/test/layer_tree_host_common_test.cc

 // Copyright 2014 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/layer_tree_host_common_test.h"
 
 #include <stddef.h>
 
 #include "cc/layers/layer.h"
 #include "cc/layers/layer_impl.h"
@@ skipping 225 matching lines @@
 };
 
 LayerTreeHostCommonTest::LayerTreeHostCommonTest()
     : LayerTreeHostCommonTestBase(LayerTreeSettingsForCommonTest()) {}
 
 LayerTreeHostCommonTest::LayerTreeHostCommonTest(
     const LayerTreeSettings& settings)
     : LayerTreeHostCommonTestBase(settings) {
 }
 
+void LayerTreeHostCommonTest::SetScrollOffsetDelta(
+    LayerImpl* layer_impl,
+    const gfx::Vector2dF& delta) {
+  layer_impl->SetCurrentScrollOffset(
+      layer_impl->synced_scroll_offset()->ActiveBase() +
+      gfx::ScrollOffset(delta));
+}
+
 }  // namespace cc