Make toPositionInFlatTree() to handle a position anchored by shadow root

third_party/WebKit/Source/core/editing/PositionTest.cpp

Index: third_party/WebKit/Source/core/editing/PositionTest.cpp
diff --git a/third_party/WebKit/Source/core/editing/PositionTest.cpp b/third_party/WebKit/Source/core/editing/PositionTest.cpp
index 97c036feea3e7f50af452ae4ea0c2a26563d0e98..1c775caac98960370a10dda4f6e9983e7667c1c9 100644
--- a/third_party/WebKit/Source/core/editing/PositionTest.cpp
+++ b/third_party/WebKit/Source/core/editing/PositionTest.cpp
@@ -139,6 +139,14 @@ TEST_F(PositionTest, ToPositionInFlatTreeWithShadowRoot)
 
     EXPECT_EQ(PositionInFlatTree(host, 0), toPositionInFlatTree(Position(shadowRoot, 0)));
     EXPECT_EQ(PositionInFlatTree(host, PositionAnchorType::AfterChildren), toPositionInFlatTree(Position(shadowRoot, 1)));
+    EXPECT_EQ(PositionInFlatTree(host, PositionAnchorType::AfterChildren),
+        toPositionInFlatTree(Position(shadowRoot, PositionAnchorType::AfterChildren)));
+    EXPECT_EQ(PositionInFlatTree(host, PositionAnchorType::BeforeChildren),
+        toPositionInFlatTree(Position(shadowRoot, PositionAnchorType::BeforeChildren)));
+    EXPECT_EQ(PositionInFlatTree(host, PositionAnchorType::AfterAnchor),
+        toPositionInFlatTree(Position(shadowRoot, PositionAnchorType::AfterAnchor)));
+    EXPECT_EQ(PositionInFlatTree(host, PositionAnchorType::BeforeAnchor),
+        toPositionInFlatTree(Position(shadowRoot, PositionAnchorType::BeforeAnchor)));
 }
 
 TEST_F(PositionTest, ToPositionInFlatTreeWithShadowRootContainingSingleContent)