cc: Clean up root_layer code in LTI

cc/trees/layer_tree_host_unittest_picture.cc

 // Copyright 2013 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/trees/layer_tree_host.h"
 
 #include "cc/test/fake_content_layer_client.h"
 #include "cc/test/fake_picture_layer.h"
 #include "cc/test/fake_picture_layer_impl.h"
 #include "cc/test/layer_tree_test.h"
@@ skipping 58 matching lines @@
         // Active while there are pending and active twins again.
         layer_tree_host()->SetNeedsCommit();
         break;
       case 5:
         EndTest();
         break;
     }
   }
 
   void WillActivateTreeOnThread(LayerTreeHostImpl* impl) override {
-    LayerImpl* active_root_impl = impl->active_tree()->root_layer();
+    LayerImpl* active_root_impl = impl->active_tree()->root_layer_for_testing();
     int picture_id = impl->active_tree()->source_frame_number() < 2
                          ? picture_id1_
                          : picture_id2_;
 
     if (!impl->pending_tree()->LayerById(picture_id)) {
       EXPECT_EQ(2, activates_);
       return;
     }
 
     FakePictureLayerImpl* pending_picture_impl =
@@ skipping 192 matching lines @@
     }
   }
 
   void WillActivateTreeOnThread(LayerTreeHostImpl* impl) override {
     LayerImpl* child = impl->sync_tree()->LayerById(picture_->id());
     FakePictureLayerImpl* picture_impl =
         static_cast<FakePictureLayerImpl*>(child);
     PictureLayerTiling* tiling = picture_impl->HighResTiling();
     int num_tiles_y = tiling->TilingDataForTesting().num_tiles_y();
 
-    if (!impl->active_tree()->root_layer()) {
+    if (!impl->active_tree()->root_layer_for_testing()) {
       // If active tree doesn't have the layer, then pending tree should have
       // all needed tiles.
       EXPECT_TRUE(tiling->TileAt(0, 0));
     } else {
       // Since there was no invalidation, the pending tree shouldn't have any
       // tiles.
       EXPECT_FALSE(tiling->TileAt(0, 0));
     }
     EXPECT_FALSE(tiling->TileAt(0, num_tiles_y));
 
@@ skipping 260 matching lines @@
   int last_frame_drawn_;
   bool ready_to_draw_;
 };
 
 // Multi-thread only because in single thread you can't pinch zoom on the
 // compositor thread.
 MULTI_THREAD_TEST_F(LayerTreeHostPictureTestRSLLMembershipWithScale);
 
 }  // namespace
 }  // namespace cc