Ensure the viewport is always represented by the inner viewport layer.

cc/trees/layer_tree_host_unittest.cc

Index: cc/trees/layer_tree_host_unittest.cc
diff --git a/cc/trees/layer_tree_host_unittest.cc b/cc/trees/layer_tree_host_unittest.cc
index d7c5632ca1ebfa334235be2d5efa5e45561c6aed..e05d7535b1bddceb17b087be0d2186e01d205f1f 100644
--- a/cc/trees/layer_tree_host_unittest.cc
+++ b/cc/trees/layer_tree_host_unittest.cc
@@ -5008,7 +5008,7 @@ class LayerTreeHostTestCrispUpAfterPinchEnds : public LayerTreeHostTest {
     // pinch.
     pinch->AddChild(layer);
 
-    layer_tree_host()->RegisterViewportLayers(NULL, root, pinch, pinch);
+    layer_tree_host()->RegisterViewportLayers(NULL, root, pinch, nullptr);
     layer_tree_host()->SetPageScaleFactorAndLimits(1.f, 1.f, 4.f);
     layer_tree_host()->SetRootLayer(root);
     LayerTreeHostTest::SetupTree();
@@ -5307,7 +5307,7 @@ class LayerTreeHostTestContinuousDrawWhenCreatingVisibleTiles
     // pinch.
     pinch->AddChild(layer);
 
-    layer_tree_host()->RegisterViewportLayers(NULL, root, pinch, pinch);
+    layer_tree_host()->RegisterViewportLayers(NULL, root, pinch, nullptr);
     layer_tree_host()->SetPageScaleFactorAndLimits(1.f, 1.f, 4.f);
     layer_tree_host()->SetRootLayer(root);
     LayerTreeHostTest::SetupTree();