[runtime] Add PositiveNumberToUint32 helper to avoid double to uint roundtrip

src/objects-inl.h

 // Copyright 2012 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.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 3835 matching lines @@
 }
 
 
 template <>
 inline Vector<const uc16> String::GetCharVector() {
   String::FlatContent flat = GetFlatContent();
   DCHECK(flat.IsTwoByte());
   return flat.ToUC16Vector();
 }
 
+uint32_t String::ToValidIndex(Object* number) {
+  uint32_t index = PositiveNumberToUint32(number);
+  uint32_t length_value = static_cast<uint32_t>(length());
+  if (index > length_value) return length_value;
+  return index;
+}
 
 uint16_t SeqOneByteString::SeqOneByteStringGet(int index) {
   DCHECK(index >= 0 && index < length());
   return READ_BYTE_FIELD(this, kHeaderSize + index * kCharSize);
 }
 
 
 void SeqOneByteString::SeqOneByteStringSet(int index, uint16_t value) {
   DCHECK(index >= 0 && index < length() && value <= kMaxOneByteCharCode);
   WRITE_BYTE_FIELD(this, kHeaderSize + index * kCharSize,
@@ skipping 4619 matching lines @@
 #undef WRITE_INT64_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_OBJECTS_INL_H_