Rewrite references to "wtf/" to "platform/wtf/" in core/layout.

third_party/WebKit/Source/core/layout/api/SelectionState.cpp

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/layout/api/SelectionState.h"
 
-#include "wtf/Assertions.h"
+#include "platform/wtf/Assertions.h"
 
 namespace blink {
 
 std::ostream& operator<<(std::ostream& out, const SelectionState state) {
   static const char* const kText[] = {
 #define V(state) #state,
       FOR_EACH_SELECTION_STATE(V)
 #undef V
   };
 
   const auto& it = std::begin(kText) + static_cast<size_t>(state);
   DCHECK_GE(it, std::begin(kText)) << "Unknown state value";
   DCHECK_LT(it, std::end(kText)) << "Unknown state value";
   return out << *it;
 }
 
 }  // namespace blink