Clean LayerImpl's scroll offset callers in unit tests.

cc/test/layer_tree_host_common_test.cc

Index: cc/test/layer_tree_host_common_test.cc
diff --git a/cc/test/layer_tree_host_common_test.cc b/cc/test/layer_tree_host_common_test.cc
index cbad7e897b476914a4d2e6603865812aa52c78b2..80521fc9adbaf019e34ce4cdb3ca1326af248368 100644
--- a/cc/test/layer_tree_host_common_test.cc
+++ b/cc/test/layer_tree_host_common_test.cc
@@ -243,4 +243,12 @@ LayerTreeHostCommonTest::LayerTreeHostCommonTest(
     : 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