Refactor SetViewportLayerIds to use a struct instead of 6 values

cc/test/test_layer_tree_host_base.cc

 // Copyright 2016 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/test_layer_tree_host_base.h"
 
 #include "base/memory/ptr_util.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "cc/test/fake_compositor_frame_sink.h"
 #include "cc/test/fake_raster_source.h"
@@ skipping 114 matching lines @@
             .release()));
     if (!tile_size.IsEmpty())
       pending_layer->set_fixed_tile_size(tile_size);
   }
   pending_root->test_properties()->force_render_surface = true;
   // The bounds() just mirror the raster source size.
   pending_layer->SetBounds(raster_source->GetSize());
   pending_layer->SetRasterSourceOnPending(raster_source, invalidation);
 
   pending_root->test_properties()->AddChild(std::move(pending_layer));
-  pending_tree->SetViewportLayersFromIds(
-      Layer::INVALID_ID, pending_tree->root_layer_for_testing()->id(),
-      Layer::INVALID_ID, Layer::INVALID_ID, Layer::INVALID_ID,
-      Layer::INVALID_ID);
+  LayerTreeImpl::ViewportLayerIds viewport_ids;
+  viewport_ids.page_scale = pending_tree->root_layer_for_testing()->id();
+  pending_tree->SetViewportLayersFromIds(viewport_ids);
 
   pending_layer_ = static_cast<FakePictureLayerImpl*>(
       host_impl()->pending_tree()->LayerById(id_));
 
   // Add tilings/tiles for the layer.
   bool update_lcd_text = false;
   RebuildPropertyTreesOnPendingTree();
   host_impl()->pending_tree()->UpdateDrawProperties(update_lcd_text);
 }
 
@@ skipping 36 matching lines @@
   state.hard_memory_limit_in_bytes = state.soft_memory_limit_in_bytes * 2;
   state.memory_limit_policy = ALLOW_ANYTHING;
   state.tree_priority = SAME_PRIORITY_FOR_BOTH_TREES;
 
   host_impl_->resource_pool()->SetResourceUsageLimits(
       state.soft_memory_limit_in_bytes, state.num_resources_limit);
   host_impl_->tile_manager()->SetGlobalStateForTesting(state);
 }
 
 }  // namespace cc