Move platform abstraction to base library

src/conversions.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_CONVERSIONS_H_
 #define V8_CONVERSIONS_H_
 
 #include <limits>
 
-#include "src/checks.h"
+#include "src/base/logging.h"
 #include "src/handles.h"
 #include "src/objects.h"
 #include "src/utils.h"
 
 namespace v8 {
 namespace internal {
 
 class UnicodeCache;
 
 // Maximum number of significant digits in decimal representation.
@@ skipping 203 matching lines @@
                            Object* number) {
   size_t result = 0;
   bool is_valid = TryNumberToSize(isolate, number, &result);
   CHECK(is_valid);
   return result;
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_CONVERSIONS_H_