Bug fix: StyledMarkupSerializer's m_lastClosed can be null

Source/core/editing/StyledMarkupSerializerTest.cpp

Index: Source/core/editing/StyledMarkupSerializerTest.cpp
diff --git a/Source/core/editing/StyledMarkupSerializerTest.cpp b/Source/core/editing/StyledMarkupSerializerTest.cpp
index 53822e6b1d6963b356e1f22da42ee7acbcfa3912..f09cc28b77880c967726613cdc3de1c353f3746c 100644
--- a/Source/core/editing/StyledMarkupSerializerTest.cpp
+++ b/Source/core/editing/StyledMarkupSerializerTest.cpp
@@ -205,4 +205,12 @@ TEST_F(StyledMarkupSerializerTest, StyleDisplayNone)
     EXPECT_EQ(expectedResult, serialize<EditingInComposedTreeStrategy>());
 }
 
+TEST_F(StyledMarkupSerializerTest, StyleDisplayNoneAndNewLines)
+{
+    const char* bodyContent = "<div style='display:none'>11</div>\n\n";
+    setBodyContent(bodyContent);
+    EXPECT_EQ("", serialize<EditingStrategy>());
+    EXPECT_EQ("", serialize<EditingInComposedTreeStrategy>());
+}
+
 } // namespace blink