Remove some unnecessary using namespaces and add include guards

third_party/WebKit/Source/core/layout/ColumnBalancer.h

Index: third_party/WebKit/Source/core/layout/ColumnBalancer.h
diff --git a/third_party/WebKit/Source/core/layout/ColumnBalancer.h b/third_party/WebKit/Source/core/layout/ColumnBalancer.h
index a963e5a069d2e3f9303e5a9db07b97ffc8024b6e..b130086357dd6c0df6d558389fad835469abdf44 100644
--- a/third_party/WebKit/Source/core/layout/ColumnBalancer.h
+++ b/third_party/WebKit/Source/core/layout/ColumnBalancer.h
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#ifndef ColumnBalancer_h
+#define ColumnBalancer_h
+
 #include "core/layout/LayoutMultiColumnSet.h"
 
 namespace blink {
@@ -270,3 +273,5 @@ class MinimumSpaceShortageFinder final : public ColumnBalancer {
 };
 
 }  // namespace blink
+
+#endif  // ColumnBalancer_h