Get rid of two callsites of effect_tree.FindNodeIndexFromOwningLayerId.

cc/trees/damage_tracker_unittest.cc

Index: cc/trees/damage_tracker_unittest.cc
diff --git a/cc/trees/damage_tracker_unittest.cc b/cc/trees/damage_tracker_unittest.cc
index e1c292539f3b9cd8e92f52e5d18dbe729233f17e..d036723038efb67ffdadfc18d6fe16329c00a494 100644
--- a/cc/trees/damage_tracker_unittest.cc
+++ b/cc/trees/damage_tracker_unittest.cc
@@ -207,8 +207,8 @@ TEST_F(DamageTrackerTest, SanityCheckTestTreeWithTwoSurfaces) {
   EXPECT_TRUE(GetRenderSurface(root)->damage_tracker()->GetDamageRectIfValid(
       &root_damage_rect));
 
-  ASSERT_TRUE(GetRenderSurface(child1));
-  EXPECT_FALSE(GetRenderSurface(child2));
+  EXPECT_NE(GetRenderSurface(child1), GetRenderSurface(root));
+  EXPECT_EQ(GetRenderSurface(child2), GetRenderSurface(root));
   EXPECT_EQ(3, GetRenderSurface(root)->num_contributors());
   EXPECT_EQ(2, GetRenderSurface(child1)->num_contributors());
 
@@ -1105,7 +1105,7 @@ TEST_F(DamageTrackerTest, VerifyDamageForAddingAndRemovingRenderSurfaces) {
   EmulateDrawingOneFrame(root);
 
   // Sanity check that there is only one surface now.
-  ASSERT_FALSE(GetRenderSurface(child1));
+  ASSERT_EQ(GetRenderSurface(child1), GetRenderSurface(root));
   ASSERT_EQ(4, GetRenderSurface(root)->num_contributors());
 
   EXPECT_TRUE(GetRenderSurface(root)->damage_tracker()->GetDamageRectIfValid(